The distributions of taurine-like and GABA-like immunoreactivities in the rat cerebellum were compared by analysis of consecutive semithin and ultrathin sections, postembedding labeled with the peroxidase-antiperoxidase technique or with an indirect immunogold procedure, respectively. Taurine-like immunoreactivity was selectively enriched in Purkinje cell bodies, dendrites and spines, and boutons in the cerebellar nuclei exhibiting ultrastructural features typical of Purkinje cell terminals. The stellate and basket cell bodies and terminals were very weakly labeled. A computer assisted quantitative assessment of the net immunogold labeling revealed that the mean gold particle density in the Purkinje cell terminals was about 70% higher than that in the Purkinje cell dendrites, and about 14 times higher than that in the stellate/basket cell terminals in the molecular layer. Stellate, basket and Purkinje cell terminals emerged as intensely immunoreactive in adjacent sections processed with an antiserum against conjugated GABA. These findings indicate, contrary to recent electrophysiological data, that GABA is a more likely transmitter candidate than taurine in the stellate cells. The apparent colocalization of GABA and taurine in the terminals of Purkinje cells raises the possibility that these terminals are capable of releasing two different inhibitory amino acids.