The effects of prostaglandin (PG) E2 on renal fluid and electrolyte excretion were investigated in pentobarbital anesthetized dogs. PGE2 (0.01 μg/min per kilogram of body weight) increased renal blood flow (RBF), urinary sodium excretion [ ], and urinary potassium excretion [ ] and decreased the ratio of the outer to inner cortical blood flows (OC:IC) as measured by radionuclide labelled microspheres. To determine whether these effects are mediated through hemodynamic or direct tubular changes, acetylcholine (ACh, 2 μg/min per kilogram of body weight) was infused before and during the administration of PGE2 (ACh + PGE2) to eliminate the hemodynamic responses to PGE2. Infusion of ACh alone induced renal vasodilatation, a diuresis, natriuresis, and kaliuresis. The infusion of ACh + PGE2 produced an additional 61% increase in the urinary flow rate (V), a 93% rise in [ ], and a 40% enhancement of [ ] when compared with ACh alone. There were no changes in RBF, OC:IC, glomerular filtration rate, or filtration fraction between the infusions of ACh and ACh + PGE2. The further increases in V, [ ], and [ ] during ACh and PGE2 suggest that PGE2 has a direct inhibitory effect on the tubular transport of electrolytes in the canine kidney.