The pancreatic glucagon (IRG) secretion pattern was studied during a 2 h glucose infusion test (12 mg/kg/min) in 21 controls as well as in 44 subjects showing different degrees of carbohydrate intolerance. The fasting IRG levels increased significantly from controls (98 +/- 7.6 pg/ml) to chemical (144 +/- 9 pg/ml) and mild maturity-onset-type diabetics (166 +/- 12.2 pg/ml). During artificial hyperglycaemia the glucagon concentrations decreased slightly in all groups, but they remained at a higher level in early and overt diabetics). The molar IRI-IRG ratios have been found to be diminished in patients displaying a disturbed carbohydrate tolerance. There was not any correlation between insulin and glucagon concentrations in the blood. The findings suggest that abnormalities of alpha cell function may be present in early and overt diabetes independent of beta cell responsiveness. The causal relationship of A and B cell function in glucose intolerant subjects has to be cleared in follow-up studies.