1. Glomerular filtration rate and effective renal blood-flow were normal in a series of patients with sickle cell anaemia. Fractional creatinine excretion and fractional urea excretion were increased.
2. During indomethacin administration there were significant falls in glomerular filtration rate, effective renal blood-flow, creatinine clearance and urea clearance in the patients with sickle cell anaemia; fractional urea excretion also fell markedly. In control subjects none of these variables changed after indomethacin.
3. Serum concentration of urea rose markedly during indomethacin administration in sickle cell anaemia, owing to both the decrease in glomerular filtration rate and the increase in fractional urea reabsorption.
4. We conclude that prostaglandins have an important role in maintaining a normal glomerular filtration rate and effective renal blood-flow in sickle cell anaemia. The abnormal urea handling in patients with this disease remains to be elucidated.