The interface between two cells from the immune system has recently been coined "immunological synapse". The authors review recent findings concerning the structure of the synapse formed between T lymphocytes and antigen-presenting cells. T cells can be part of different synapses, depending on the antigen-presenting cell (B cell hybridoma, proteo-lipid bilayer, macrophage, dendritic cell). The synapse formed with dendritic cells is discussed in more details. A comparison is made with the synapses from the nervous system. Several parallel questions are discussed: how receptors can be clustered, what is the influence of synapse functioning on the structure of the synapse. It is suggested that in both cases two modes of communication exist in parallel: direct cell-cell contacts and soluble mediators, neurotransmitters in one case, putative immunotransmitters in the other.