N,N'-Dimethylurea (DMU) at 4 g/kg i.p. protected against the normal rise in blood glucose associated with alloxan-induced diabetes when it was administered to mice at 30 min or 2 hr prior to the i.v. injection of 75 mg/kg of alloxan. Blood glucose measurements were made 72 h post alloxan. At 30 min after the above dose of DMU alone (no alloxan) there was a significant rise in blood glucose but at 2 h after DMU there was no significant difference between control and DMU-treated animals. These data indicate that the primary mode of protection by DMU does not involve a rise in blood glucose. The data however are consistent with another mode of protection by DMU such as its scavenging of the hydroxyl radical, a cytotoxic species which can be generated from alloxan through a series of reactions.