In situ hybridization histochemistry using cDNA oligonucleotide probes for the neuropeptides dynorphin, enkephalin and substance P was used to map the distribution of peptidergic neurons in the striatal patch and matrix compartments in the rat. Striatal neurons containing message for each of these peptides were distributed in both striatal compartments in the following proportions: dynorphin, in 52% of patch neurons and 45% of matrix neurons; enkephalin, in 65% of patch neurons and 58% of matrix neurons and substance P, in 61% of patch neurons of 54% matrix neurons. Fluorescent retrograde axonal tracing combined with in situ hybridization histochemistry demonstrated that the majority of neurons expressing enkephalin project to the globus pallidus and few project to the substantia nigra, whereas the reverse obtains for neurons expressing dynorphin and substance P.