In the cat visual cortex, almost all parvalbumin-positive cells are GABAergic, and about 80% of the calbindin D-28K-positive neurons are also GABA-immunoreactive. About 37% of the GABAergic neurons contain parvalbumin and a smaller fraction (about 18%) contains calbindin. Furthermore, parvalbumin and calbindin are localized in two separate neuronal populations in the cat visual cortex, suggesting that two GABAergic populations can be distinguished, one containing parvalbumin and one containing calbindin. Double staining for parvalbumin and neuropeptides (CCK, SRIF and NPY), revealed no double-labeled cells, with the exception of a few SRIF- and parvalbumin-positive neurons. These results show that cortical GABAergic cells can be differentiated on basis of their calcium binding protein and neuropeptide immunoreactivity.