Lead interferes with cellular energy metabolism by inhibiting ATP (Adenosine triphosphate) synthesis and hydrolysis. This study was conducted to determine in vitro effects of lead on Na+, K+-ATPase activity in four regions of adult rat brain: the cerebellum, the hippocampus, the frontal cortex and the brain stem. Male rats (Wistar strain) weighing 125-150 g were sacrificed, whole brain excised and the four regions were isolated. Each tissue was homogenized separately in sucrose (0.25 M) and imidazole (10 mM) buffer (pH 7.5) and P2 fraction was prepared by following established methods. The activity of ATPase was determined by measuring inorganic phosphate (Pi) liberated from ATP hydrolysis. The delineation of Na+, K+-activated component of ATPase was obtained by the difference between total ATPase and Mg2+-ATPase using 1 mM ouabain. The P2 fraction was incubated with 0, 5, 10, 25, 50 and 100 microM of lead at 37 degrees C for 10 min. The enzyme activity was expressed as micromoles of Pi liberated/mg protein/hr. The results indicated a concentration-dependent and region-specific response to lead. In vitro lead at 50 and 100 microM significantly inhibited ATPase activity in all regions of the brain. It was also observed that in the control rats, the enzyme activity was high in cerebellum and hippocampus regions of the brain. In vitro dithiothreitol (DTT) protected the enzyme activity from IC50 lead in four regions of brain. In cerebellum and hippocampus, a 5 microM DTT provided 100% protection against IC50 lead. These results suggest that lead interferes with the ion transport mechanism and cellular energy metabolism of the brain and this effect is region specific.