Treatment of pregnant rats with methylazoxymethanol (MAM) at day 15 of gestation induces a marked microencephaly in the offspring, characterized by impaired formation of interneurons in the areas affected. We have measured somatostatin immunoreactivity in the cortex, striatum and hippocampus of the offspring of pregnant rats treated with graded doses of MAM. A long-lasting increase in the cortical levels of this peptide was found, suggesting that somatostatinergic interneurons might be selectively spared by administration of the cytotoxic agent at this gestational age.