The brain volumes of 8 male Australian Aborigines and 11 male Caucasians were determined. Total brain volume was significantly smaller for Aborigines (1199 +/- 84 ml) compared to Caucasians (1386 +/- 98 ml). Significantly smaller volumes were also found for cerebellum, prosencephalon-mesencephalon unit, cerebral cortex, frontal cortex, parieto-occipitotemporal cortex, and hippocampus. Volumes of ponsmedulla oblongata unit (21 +/- 3 ml for Aborigines and 22 +/- 3 ml for Caucasians) and visual cortex (14.9 ml +/- 2.6 ml and 14.6 +/- 2.2 ml, respectively) did not differ significantly. The striate cortex extended further onto the lateral surface of the occipital lobe in Aboriginal brains. The frontal portion of cerebral cortex was larger in Aboriginal than in Caucasian brains. According to the specific growth periods for the areas studied, these differences could be explained by the higher incidence of malnutrition and infectious diseases for Aboriginals during the development of the brain in early childhood, especially after the 6th postnatal month. However, genetic influences cannot be excluded. The results for the visual cortex of Aborigines might represent an adaptation to living conditions in the bush and desert regions of Australia.