Shortened red cell life span and excess iron cause functional and physiological abnormalities in various organ systems in thalassemia patients. In an earlier study, we showed that beta-thalassemia patients have a high prevalence of renal tubular abnormalities. The severity correlated with the degree of anemia, being least severe in patients on hypertransfusion and iron chelation therapy, suggesting that the damage might be caused by the anemia and increased oxidation induced by excess iron deposits. This study was designed to define the renal abnormalities associated with alpha-thalassemia and to correlate the renal findings with clinical parameters. Thirty-four pediatric patients (mean age 8.2+/-2.8 years) with Hb H disease or Hb H/Hb CS were studied. Ten patients (group 1) were splenectomized, with a mean duration post splenectomy of 3.5+/-1.4 years; 24 patients (group 2) had intact spleens. The results were compared with 15 normal children. Significantly higher levels of urine N-acetyl-beta- d-glycosaminidase, malondialdehyde (MDA), and beta(2)-microglobulin were found in both groups compared with normal children. An elevated urine protein/creatinine ratio was recorded in 60% of group 1 and 29% of group 2. Two patients (5.9%), 1 in each group, had generalized aminoaciduria. We found proximal tubular abnormalities in alpha-thalassemia patients. Increased oxidative stress, possibly iron induced, may play an important role, since urine MDA levels were significantly increased in both groups of patients.