OBJECTIVE Adiponectin is an adipose tissue-specific protein with antiatherogenic and insulin-sensitizing properties. In patients with essential hypertension, plasma adiponectin concentrations are lower than in healthy subjects. Antihypertensive drugs do not uniformly influence components of the metabolic syndrome. Therefore, the aim of this study was to evaluate the influence of 6 months' monotherapy with different antihypertensive drugs on plasma adiponectin concentration in essential hypertension patients. METHODS Forty essential hypertension patients were randomized to receive enalapril, metoprolol, amlodipine or indapamide. Plasma concentrations of adiponectin, insulin, glucose and body fat content were estimated twice: before and after 6 months of antihypertensive monotherapy. RESULTS Plasma adiponectin concentration did not change significantly after enalapril (11.5 +/- 4.8 vs. 11.1 +/- 4.1 mg/l), metoprolol (10.2 +/- 4.2 vs. 9.8 +/- 4.5 mg/l), and amlodipine (9.0 +/- 6.0 vs. 8.5 +/- 5.4 mg/l) treatment. However, a significant decrease of plasma adiponectin concentration (from 11.6 +/- 4.6 to 10.2 +/- 4.2 mg/l, p = 0.047) was observed in patients treated with indapamide. Additionally in these patients, a significant increase of the HOMA-IR index was found (p = 0.021). CONCLUSIONS Treatment with indapamide was followed by a significant decrease of plasma adiponectin concentration. This may participate in the pathogenesis of carbohydrate metabolism disturbances often found in patients treated with thiazide-type diuretics.