3H-Glycine was released by 50 mM K+ in a calcium-dependent manner from rat substantia nigra slices. This release was abolished by GABA (0.1-1 mM) and muscimol (0.1 mM). Taurine and beta-alanine were without effect on evoked 3H-glycine release. The effect of GABA (0.5 mM) was reversed picrotoxin (50 micro M). These results support the hypothesis that GABA receptors may be present on glycinergic interneurones in the substantia nigra.