Fructosamine values, and the influence thereon of age, BMI and sex, were determined in 384 nondiabetic individuals aged between 20 and 95 years. In this control group mean F levels were 2.45 +/- 0.25 mmol/l and were age-related only, rising from 2.3 in the second decade to 2.6 in the eighth. We compared F and HbA1c in 135 diabetic patients. F correlated with HbA1c in the diabetic group (r = 0.76, p less than 0.001). Because of its biological properties fructosamine could become a useful pointer in the metabolic follow-up of diabetic patients, especially where clinic visits are frequent.