An experiment was undertaken to determine whether an overdose of the anthelmintic parbendazole could cause paralysis in lambs when given to ewes during the early stages of pregnancy. Out of a total of 68 lambs, born from ewes treated at various stages of gestation with parbendazole at 180 mg/kg, 5 showed the paralysis syndrome, 5 showed skeletal deformities, 2 were ataxic, while 1 foetus was aborted. The ewes giving birth to paralysed lambs had been treated with parbendazole at 30, 32, 37 and 53 days of gestation. Cerebral hypoplasia was observed in 2 of these lambs, while 2 others showed internal hydrocephaly. Histopathological lesions observed in the lambs with cerebral hypoplasia included gliosis and areas of encephalomalacia in the cerebral white matter. Lesions present in the spinal cords of the 2 ataxic lambs included pydromyelia, syringomyelia, duplication of the spinal canal and an abnormal position of the canal. This is the first report describing brain lesions in lambs as a result of an overdose of parbendazole.