The effects of perinatal lead administration on developing rat brain were studied by using cerebellar grafts in oculo. With 1% lead acetate in the drinking water, little change was seen in the histological organization of the graft. In marked contrast, virtually all Purkinje cell spontaneous discharge was absent in these grafts. This was seen even though 4-5 months had elapsed between the recording and the cessation of lead treatment. There was no alteration in electrophysiological properties of transplant Purkinje cells from sodium acetate-treated animals. Moreover, host in situ cerebellar Purkinje cells in both groups of animals discharged normally. These data indicate that lead administration, to elicit blood levels of 450-550 micrograms/liter, produces a long-lasting selective electrophysiological deficit in developing brain in oculo.