The caudate-putamen-complex of adult rat was investigated by means of the rapid Golgi impregnation technique. Untreated rats and rats with unilateral lesions of the MFB were analysed. Four aspiny neuron types and types extremely sparse in spines, resp., could be demonstrated: Aspiny giant neurons, aspiny spindle-shaped neurons, aspiny spidery neurons and neuroglioform neurons. The spine-less neuron types of the caudate putamen which can be differentiated according to morphological criteria are tempted to be classified in a functional manner. Especially based on the axon morphology, the giant neurons are considered to be projective neurons; the other cell types are, in all probability, neostriatal interneurons. The type 2 neurons (spindle-shaped neurons) which are regarded to be absolutely autonomous cell types do represent the vast majority of the population of the aspiny neurons of the caudate-putamen-complex. Comparing the findings laid down here with those of AChE-histochemistry after DFP treatment may permit conclusions with respect to the functional role of aspiny neurons within the neostriatum of the rat.