Arterial hypertension, which represents a common problem in patients with renal transplant, contributes to the cardiovascular morbidity and mortality of these patients. The most usual immunosuppressive drugs (cyclosporine and FK-506) collaborate on the development of hypertension. Calcium channel blockers are the most habitually used antihypertensive drugs in this population, although its long-term hemodimamycs effects could be deleterious especially in transplanted patients with chronic graft nephropathy. Losartan, a specific blocker of angiotensin II (AT1) receptors, has demonstrated a potent antihypertensive effect with a good safety and tolerance profile. The glomerular effects of losartan could be useful in transplanted patients. The present open, prospective and multicenter study evaluated the efficacy and safety of losartan in the treatment of hypertension in a group of patients with a renal transplant. Seventy-six patients with systolic blood pressure > or = 140 and/or diastolic blood pressure > or = 90 mm Hg, and/or patients on therapy with one antihypertensive drug and related side effects were included. After inclusion, therapy with losartan 50 mg/24 hr was started, discontinuing the previous antihypertensive therapy and/or therapy which caused the side effects. At four weeks, if blood pressure (BP) was not controlled, hydrochlorothiazide 25 mg or furosemide 40 mg/24 hr was added. At baseline and at weeks 2, 4, 8 and 12, the following parameters were monitored: BP, creatinine, hematocrit, hemoglobin, glucose, ions, uric acid, cholesterol, triglycerides, bilirubin, SGOT, SGPT, GGT, LDH, calcium, phosphate, alkaline phosphatase, proteinuria, and both cyclosporine and FK-506 levels in whole blood. Sixty-seven patients completed the 12-week study period. Mean blood pressure decreased from 113 +/- 10 to 102 +/- 9 mm Hg at the end of the study (P < 0.0001); 38 of the 67 patients (56.7%) who completed the study had a SBP lower than 140 mm Hg and a DBP lower than 90. These blood pressures were obtained in 30 patients on monotherapy with losartan (78.9%). Proteinuria decreased significantly at week 4 and was confirmed at week 12, especially in patients with proteinuria > or = 300 mg/24 hr. Nine patients were withdrawn during the study period for different reasons. Serum creatinine showed a slight, non-clinically significant increase at week 4, remaining stable until the end of the study. Two patients developed a mild normocytic anemia, and three others presented a mild impairment of pre-existent anemia. No interactions with cyclosporine or FK-506 were described. These results indicate that losartan is effective in reducing BP in hypertensive patients with a renal transplant. It has a good tolerance profile and does not interfere with immunosuppressive therapy.