The insulin-sensitising adipose hormone adiponectin is reduced in type 2 diabetic patients. We assessed the relationships between plasma adiponectin and chronic hyperglycaemia. Adiponectin levels and glycated haemoglobin (HbA1c) were measured at enrolment and after 90 days in 16 patients with type 2 diabetes aged (mean +/- SEM) 63.0 +/- 0.6 years, with body mass index (BMI) 30.2 +/- 0.5 kg/m2 and HbA1c concentration 7.4 +/- 0.1%, who did not modify their hypoglycaemic treatment during the observation period. Furthermore, plasma adiponectin was measured in 29 adult patients with type 1 diabetes and compared with 29 control subjects matched for sex, age, BMI, waist circumference and bioimpedance-estimated fat mass. In type 2 diabetic patients at enrolment, adiponectin concentration correlated with BMI (r = -0.46; p < 0.05), but not with HbA1c. During the prospective observation, variations of adiponectin showed a significant correlation with variations of BMI (r = -0.47; p < 0.01), but not with variations of HbA1c concentration. These results were confirmed by multivariate analysis after adjustment for sex and age. Adiponectin levels in type 1 diabetic patients (380.8 +/- 13.7 ng/ml in women, 192.5 +/- 13.9 ng/ml in men) were significantly (p < 0.05) higher than in control subjects (277.6 +/- 11.0 ng/ml in women, 102.7 +/- 5.1 ng/ml in men); plasma adiponectin correlated significantly with BMI and waist circumference, but not with HbA1c. In conclusion, the reduction of plasma adiponectin levels in type 2 diabetic patients does not appear to be determined by chronic hyperglycaemia. Adiponectin levels are increased in type 1 diabetes, but this phenomenon is not attributable to differences in nutritional status or body composition.