The effect of different dietary fats with varying degrees of unsaturation and essential fatty acid composition, which are commonly consumed in India, on the activity of some important membrane-bound enzymes was assessed in different brain regions of rat. Four groups of male CFY weanling rats were fed nutritionally adequate diets containing groundnut, coconut, safflower or mustard oil as fat source at 20% level for 16 weeks. The synaptosomal, microsomal and myelin membranes were prepared from three brain regions, viz., cerebrum, cerebellum and brain stem from each group. The activities of Na+, K(+)-ATPase, Mg(2+)-ATPase and acetylcholinesterase were assayed and the fatty acid composition was determined in these subcellular membrane fractions. The safflower oil-fed group showed higher Na+, K(+)-ATPase activity in most membrane fractions than the coconut or mustard oil-fed groups. The Mg(2+)-ATPase activity was found to be similar amongst all groups in all the brain regions. The synaptosomal acetylcholinesterase activity was distinctly higher in coconut and groundnut oil-fed groups when compared to safflower or mustard oil consuming groups. Alterations in the activities of these subcellular membrane-bound enzymes are expected to exert a significant impact on the electrophysiological and metabolic functions of brain. Results of the present study show that depending on the nature of dietary fat the fatty acid composition of subcellular membranes is altered, which in turn could regulate the activity of membrane-bound enzymes that are vital for brain function.