In recent years, it has been demonstrated that losartan lowers macroproteinuria in diabetic or non-diabetic renal transplant recipients (RTx) similar to angiotensin converting enzyme (ACE) inhibitors. Microalbuminuria (MAU) may reflect subclinical hyperfiltration damage of the glomerulus. It could be a marker of kidney dysfunction in renal transplantation. The aim of the study was to assess the efficacy of losartan in hypertensive RTx with MAU. This study was conducted in 17 (M/F: 4/13) stable RTx. No change was made in the medical treatment of the patients. All cases received 50 mg/day losartan therapy for 12 wk. Renal functions and MAU were determined 12 and 6 wk and just before the treatment as well as sixth and twelfth week of the treatment in all patients. Losartan satisfactorily lowered systemic blood pressure. A significant reduction in MAU was observed from 103 +/- 53 mug/min at the beginning to 59 +/- 25 mug/min in the sixth week and 47 +/- 24 mug/min in the twelfth week (p = 0.0007 and 0.0005, respectively). From the sixth week of the treatment, the therapy significantly decreased hemoglobin, hematocrit and erythrocyte levels but did not change mean leukocyte and platelet counts, urea, creatinine levels and creatinine clearances. No serious side-effect was observed,during the study.