THE impairment of renal concentration during hydropenia in patients with sickle-cell disease has been recognized for several years.1-5 Although other renal abnormalities have been reported, such as proteinuria,6 hematuria,7,8 nephrotic syndrome,9 glomerulonephritis,10 and papillary necrosis,11 the hyposthenuria is by far the most commonly found dysfunction. It occurs in all patients with sickle-cell anemia and in most patients with sickle-cell trait, though usually to a lesser degree.12 Because of this impairment of renal concentration, patients with sickle-cell disease characteristically excrete large quantities of urine. We have been impressed repeatedly by the ease with which these patients undergo dehydration, both in the steady state and in sickle-cell crisis. Consequently, we have investigated the role of fluid balance in randomly selected patients with various types of sickle-cell disease. Clinical Material and Methods Twenty-four Negro subjects with sickle-cell disease were selected for study in the steady state and in sickle-cell crisis. Consequently, we