Benzimidazole compounds have teratogenic effects in domestic and experimental animals. In this study, 14 Manchega ewes were treated orally, under controlled conditions, with 20 mg netobimin (a prodrug of a benzimidazole compound) per/kg bodyweight on the 17th day of pregnancy. Congenital malformations and abortions affected 60 per cent of the lambs. The main malformations were skeletal and renal, but vascular malformations were observed for the first time. The abnormalities were investigated using radiological, dissection and vascular injection techniques, and associations among them were recorded. The anomalies are discussed in terms of embryological considerations.