Furosemide has been reported to cause pathological changes in the intestines as a consequence of the decrease in splanchnic blood flow that it produces. In view of the pancreatic toxicities of this diuretic, it was of interest to examine the effect of the agent on blood flow to this organ. An electromagnetic flow probe, was placed around the splenic artery, a vessel which supplies a major fraction of pancreatic blood flow. Within 60 min after furosemide (1 mg/kg, iv) administration, splenic blood flow (SBF) decreased by 20% and the decrease paralleled the drug-induced diuresis. When the diuresis was prevented, the agent failed to affect SBF. Thus, furosemide causes a reduction in SBF, which appears to involve a mechanism dependent upon the volume reduction produced by the drug-induced diuresis.