The renal function in ten patients with mucocutaneous leishmaniasis treated with Glucantime (meglumine antimoniate, Rhodia) or Pentostam (Sodium Stibogluconate, Wellcome) was assessed. During the use of these drugs a defect in concentrating capacity of the kidney was observed expressed as low values of maximun urinary osmolarity and negative maximun clearance of free water in relation to tests made before treatment. The urinary concentrating capacity returned to normal in 5 of the 8 patients studied 15-30 days after the end of treatment. However the maximal urinary osmolarity values where still inferior to those obtained before treatment. In two patients there was a proteinuria above 150 mg/24 hours after antimoniais which disappeared later. The clearance of endogenous creatinine do not alter significatly with the use of these drugs. The results suggest that pentavalent antimoniais can resue in a defect in urine concentrating capacity which is partially reversible after antimonial therapy has ceased.