The presence and distribution of gamma-aminobutyric acid (GABA) degradative enzyme (GABA transaminase-succinic semialdehyde dehydrogenase) activity in the rat myenteric plexus was determined histochemically using laminar preparations of the small intestine. Blue-diformazan staining resulting from reduction of the tetrazolium salt, Nitro-BT, during GABA catabolism was present in a scattered population of ileal and jejunal myenteric ganglion cells, including those resembling multipolar type II and unipolar nerve cells. Such staining was almost completely prevented under conditions of GABA-T inhibition. These results indicate that GABA is enzymically degraded at specific sites in the rat enteric nervous system where it is proposed to have a neurotransmitter function.