We investigated the effect of inorganic lead on the interaction of immature rat astrocytes and bovine adrenal endothelial cells. The two cell types were cultured alone and in coculture in the presence or absence of lead acetate for up to 1 week. A battery of cell specific markers was used for cell identification. Newborn Sprague-Dawley rat brain astrocytes were more sensitive than bovine adrenal endothelial cells to the cytotoxic effects of 10-50 microM lead acetate, as demonstrated by a decrease in cell number and by the presence of intracellular vacuoles and detached cells. The number of astrocytes decreased to 50% of control after 4 days in culture at a concentration of 10 microM lead. In contrast, a mitogenic effect of lead was observed on the endothelial cells at this concentration, with an increase in cell number to 110% of control. In coculture, the two cell types demonstrated a distinctive cellular organization and the astrocytes were less sensitive to the cytotoxic effects of lead than when they were cultured alone. A lead-enhanced induction of a neural capillary enzyme activity, gamma-GTP, was detected histochemically in the coculture system. These results are consistent with a maturing or differentiating effect of the endothelial cells on the astrocytes, making them less susceptible to lead and mature enough to induce gamma-GTP activity in the endothelial cells.