The intemeurons of the inner retina, which Cajal called amacrine cells, are the most heterogenous class of retinal neuron, exhibiting a remarkable diversity of morphology and neurochemistry that underpins the complexity of retinal function. Using Neurobiotin tracer-coupling, the morphology, topographic distribution and dendritic interrelationships of three amacrine cell types in the rabbit retina were characterised. In addition, the amino­ acid neurotransmitter content of the coupled cells was demonstrated in wholemount retinal preparations using new antisera that were raised against paraformaldehyde conjugates of GABA and glycine, which produce consistent labelling throughout the paraformaldehyde­ fixed wholemount retina. The new antisera also enabled a comprehensive study of the density and distribution of GABAergic and glycinergic amacrine cells in the rabbit retina to be performed on retinal wholemounts, thus avoiding many of the stereological errors that are inherent in using tissue sections. Wholemount retinae were triple labelled with ethidium bromide, glycine immunocytochemistry and GABA immunocytochemistry and the cell densities counted from confocal images collected at range of inferior eccentricities from the visual streak. Like other mammals, the majority of amacrine cells of the rabbit retina contain either glycine (62%) or GABA (32%) with a small percentage containing both amino acids (2%). The remaining somata in the amacrine cell layer (4%) do not label for either glycine or GABA, and a proportion of these appear to comprise the dorsally directed amacrine cells. Even though the densities of the four groups of amacrine cells may differ between animals, their proportions are relatively constant across the inferior retina. In the rabbit retina, the nuclear dye, 4,6, diamidino-2-phenylindole (DAPI), selectively labels a third type of amacrine cell, in addition to the previously characterised type a and type b cholinergic amacrine cells. There are about 100,000 DAPI-3 amacrine cells in total, accounting for 2% of all amacrine cells in the retina and their density ranges from about 130 cells/mm2 in the far peripheral retina to 770 cells/mm2 in the visual streak. The thin varicose dendrites of the DAPI-3 amacrine cells form a convoluted dendritic tree that is symmetrically bistratified in S1/S2 and S4 of the inner plexiform layer (IPL). Tracer coupling shows that the DAPI-3 amacrine cells have a 5-fold overlap in each sublamina, with the gaps in the arborisation of each cell being occupied by dendrites of neighbouring cells. The DAPI-3 cells consistently show the strongest glycine immunoreactivity in the rabbit retina. By contrast, the All amacrine cells, which are the best characterised glycinergic cells in the retina, are amongst the most weakly labelled of the glycine-immunopositive amacrine cells. The DAPI-3 cells costratify narrowly with the cholinergic amacrine cells and the On-Off direction-selective ganglion cells, suggesting that they may play an important role in movement detection. The type 1 Polyaxonal (PAI) amacrine cell is a GABAergic amacrine cell that has two morphologically distinct types of processes which arborise diffusely in the mid-IPL: spiny dendrites that form a sparsely branched dendritic arbor, and fine varicose axon-like processes that arise from the proximal dendritic tree and form a highly branched arbor. Neurobiotin-injection reveals that the axon-like processes form an extensive arbor that covers 15-30° of the visual field. The dual morphology of the PA1 cells suggests that the cell is functionally polarised, the spiny dendritic arbor being the major region of synaptic input to the cell, and the axonal arbor the major source of synaptic output. Like many types of amacrine cells, the PAI cells show strong homologous tracer-coupling, revealing that their somata may be located in the INL (45%), IPL (50%) or GCL (5%). However, PA1 cells are highly unusual in that they also show heterologous coupling to a population of ganglion cells. There about 15,000 PAI cells which comprise only 0.3% of all amacrine cells and thus these axon-bearing amacrine cells are sparsely distributed across the retina, ranging in density from 20 cells/mm2 in the far peripheral retina to 60 cells/mm2 in the visual streak. The PAI cells share many features in common with other GABAergic amacrine cells: they are wide-field cells that are present at low densities and their processes achieve uniform coverage of the retina by the dense overlapping of their dendritic arbors (12-fold overlap) and their axonal arbors (250-fold overlap). The retroflexive amacrine cells form a novel type of GABAergic amacrine cell in the rabbit retina. The distinctive feature of these medium-field cells is an unusual style of bistratification in which the primary processes cross the IPL to first ramify in S5 and then emanate processes which migrate back to arborise in S1 of the IPL. The retroflexive cells exhibit an asymmetrical bistratification, with spiny processes in sublamina b which give rise to fine varicose processes that arborise in sublamina a, suggesting that the retroflexi ve cell may be functionally polarised and receive input in the On sublamina and make output in the Off sublamina. The sublamina b arbors of the retroflexive cell show a high degree of territoriality not seen before in mammalian amacrine cells; the processes form discreet contacts with homologously coupled cells, enabling the cells to interlock with jigsaw prec1s1on. Conversely, the sublamina a arbors of neighbouring retroflexive cells interweave to achieve uniform retinal coverage, exhibiting increasing overlap with eccentricity from the visual streak The retroflexive amacrine cells account for ~1.5% of all amacrine cells, totalling about 75,0000 cells, and range in density from 100 cells/mm2 in the far peripheral retina to 360 cells/mm2 in the visual streak. These three cell types can be added to the amacrine cell catalogue, which now accounts for about 30% of all amacrine cells in the rabbit retina. The DAPI-3, PAl and retroflexive cells exhibit centro-periphery density gradients that are comparable to other identified amacrine cell types in the rabbit retina. This, plus the constancy in the proportions of GABAergic and glycinergic amacrine cells across the retina, are consistent with the concept that a local region of the rabbit retina would contain all the different amacrine cell types in characteristic proportions, forming a functional module that would increase in size with increasing eccentricity (Yaney, 1990).