The effect of prostaglandin E1 (PGE1) on renal function was examined in 8 patients with autosomal dominant polycystic kidney disease (ADPKD) and 8 subjects with non-polycystic chronic renal disease (CRD). Intravenous PGE1 infusion (50 micrograms/hr, for 2 hrs) resulted in a significant fall in creatinine clearance in ADPKD, but not in CRD. Although PGE1 had no effect on urinary sodium excretion and osmolar clearance in both groups, it increased significantly free water clearance in CRD, but not in ADPKD. Nephrogenic cyclic AMP during PGE1 administration did not differ significantly from their respective baseline level in two groups. In these groups, although nephrogenic cyclic AMP correlated poorly with urine volume, osmolar clearance, and free water clearance, it demonstrated a significant negative correlation with creatinine clearance. Renal volume in ADPKD cases had no relation with the parameters of renal function examined during PGE1 infusion. These data demonstrate the different responses of polycystic kidneys to PGE1 compared with non-polycystic kidneys.