The number of GABA-immunoreactive [GABA(+)] neurons and synapses was determined in functionally distinct subregions delineated as rich and poor in cytochrome oxidase (CO) in the visual cortex of adult macaqua monkeys. The average numoncal density (number per unit volume, Nv of GABA(+) neurons and synapses was not significantly different between the CO-rich and -poor regions. Twenty percent of the total number of cortical neurons and 17% of the synapses were GABA(+). On average, each visual cortical neuron re ceives 3900 synapses, 660 of them being GABA(+). The latter were distributed on the target cell in a pattern that predicts the site of GABA influences in cortex. The major targets of GABA(+) synapses were dendritic shafts, comprising nearly two-thirds of the postsynaptic elements. About every fourth and every eighth GABA(+) synapse was devoted to dendritic spines and to neuronal somata, respectively. Axon initial segments, although the exclusive targets of GABA(+) cells, comprise less than 0.1% of structures postsynaptic to GABA(+) bou tons. From this distribution, we estimate that in each cubic millimeter of striate cortex there were about 20 million GABA(+) synapses on dondritic spines, 47 million on dendritic trunks, 9 million on somata, and fewer than 0.1 million on axon initial segments. The sites of influences of GABA-immunonegative [GABA(−)] synapses were different in that they target mainly dendritic spines and dendntic trunks. About two- thirds of GABA(−) synapses were on dendritic spines, and the remainder were devoted to dendntic trunks. Only a minute fraction innervate somata. We estimate that in 1 mm3 of striate cortex there were about 235 million GABA(−) synapses on spines, 133 million on dendrites, and about 2 million on somata. The propor tions of GABA(+) neurons and synapses and their target distribution did not appreciably differ from those of the visual cortex of the cat oven though the numerical den sity of neurons was 2.5 times higher in the monkey.