The ventral lateral geniculate nucleus (vLGN) of albino rats (Wistar strain) has been described histologically and histochemically. Special attention was paid to the identification of cell classes in Nissl and Golgi preparations, the afferent and efferent connections of vLGN cells and the demonstration of enzymes of energy and transmitter metabolism. Topographical aspects were taken into consideration, too. The main results can be summarized as follows: In the rat vLGN, three subnuclei can be distinguished: the lateral and medial subnucleus and the intergeniculate leaflet. In the rostral vLGN, the lateral and medial subnucleus is separated by a vertical fibre bundle which contains retinal axons. Our own experiments and findings of other groups revealed that the rat vLGN is connected with numerous brain structures. There is no efferent projection to cortical regions. Afferent fibres reach the vLGN from retina, visual cortex, superior colliculus, pretectal region, zona incerta, contralateral vLGN, dorsal raphe nucleus, locus coeruleus, mesencephalic reticular formation, vestibular and dorsal tegmental nuclei. An efferent projection has been found to superior colliculus, pretectal region, dorsal lateral geniculate nucleus, contralateral vLGN, zona incerta, pontine nuclei, suprachiasmatic nucleus, lateral terminal nucleus of the accessory optic system and intralaminar nucleus of thalamus. Comparative findings suggest that the lateral subnucleus is involved in "specific projections", whereas the medial subnucleus projects to "unspecific zones". For detailed information see text. Five classes of neurons can be distinguished in Golgi and Nissl preparations. Class 1 cells are medium-sized to large with smooth thick proximal but branched spiny distal dendrites. They are confined to the lateral subnucleus and the intergeniculate leaflet. In the lateral subnucleus, class 1 cells could be identified as geniculo-tectal relay neurons (Brauer and Schober, 1982). All other classes of neurons are spineless or sparsely spined. Class 2 cells (giant neurons) of unknown function could be found in the lateral and medial subnucleus. Class 3 cells (medium-sized multipolar neurons) can mainly be found in the medial subnucleus. They are good candidates for neurons projecting to the contralateral vLGN. Class 4 cells (bipolar neurons) occupy the ventromedial part of the medial subnucleus and are very similar to cells localized in the adjacent zona incerta. Cells belonging to this type could found to be labelled by the HRP reaction product after injection of this enzyme in the pontine region.(ABSTRACT TRUNCATED AT 400 WORDS)