Dissociated glial cells from cell-born Rat brains in primary culture were exposed to 5 X 10(-4) M pentobarbital-Na and 2.5 X 10(-5) M morphine. Only pentobarbital was found to induce a morphological change resembling a maturation into protoplasmic astrocytes. This modification was accompanied by an increase of oxygen consumption (50-75%). No evidence could be obtained for the presence of dependence on the barbiturate or morphine, but a certain degree of tolerance to pentobarbital was observed.