The tuberculum olfactorium of the adult rat was investigated by means of neurohistological, fluorescence histochemical and enzyme histochemical methods. Using the rapid Golgi impregnation technique, seven neuron types could be demonstrated which can clearly be differentiated according to morphological criteria. Using the glyoxylic acid techniques, strongly fluorescent dopamine fibers are, in different densities, visible within the various laminae. Kainic acid application into the ventral tegmental area is followed by a strikingly reduced, no more structurally associated dopamine fiber fluorescence. After DFP intoxication, only a small proportion of the neuron population of the tuberculum olfactorium does exhibit an AChE activity; the AChE containing neurons are different as to their size and shape. The findings presented here are discussed with respect to the attributability of histochemical findings to cytoarchitectural features of this brain area.