The effects of aminophylline in Mongolian gerbils subjected to unilateral carotid ligation were studied. The drug was given in varying intraperitoneal doses at varying postoperative intervals and the animals observed for 5 days for clinical signs of stroke. Doses of 100 mg per kg caused early death and were discontinued. Doses of 50 mg per kg had no significant effect on morbidity, mortality, time until death, stroke incidence or lesion size, as compared to saline given as a control. Doses of 80 mg per kg caused a higher mortality, higher morbidity, and a shorter interval to death, but a smaller infarct. Thus, aminophylline did not have a protective effect against stroke in gerbils and was actually detrimental during the first 16 hours following the carotid ligation.