The distribution of choline acetyltransferase (ChAT) and glutamate decarboxylase (GAD), and the histochemical reaction for acetylcholinesterase have been studied in the basal forebrain and globus pallidus of unoperated rats and in rats with an electrolytic lesion of the nucleus accumbens. ChAT was highly concentrated in the substriatal region, the neostriatum and the lateral part of the rostral substantia innominata. The strongest intensity of staining for acetylcholinesterase was found in the substriatal grey and the neostriatum. Very high GAD activity was found in the substantia innominata, being even slightly higher than that in the pars reticulata of the substantia nigra. The lateral preoptic area, the bed nucleus of the stria terminalis and the globus pallidus also showed high activity of GAD. After lesions of the nucleus accumbens the activity of GAD decreased significantly in the substantia innominata and in a restricted part of the rostroventral globus pallidus, but not in the other regions studied. ChAT activity and acetylcholinesterase staining were unaffected in all regions. The results indicate that a dense GABAergic projection originates in the nucleus accumbens and terminates in the rostral substantia innominata and rostroventral part of the globus pallidus. The study gives neurochemical support to the suggestion that nucleus accumbens may be regarded as a ventral part of the neostriatum and that the rostral substantia innominata may be regarded as a ventral part of the globus pallidus.