The effect of furosemide on secretin-stimulated pancreatic secretion was examined in 12 normal subjects using a perfusion method to quantitate pancreatic output. During continuous secretin infusion (0.9 U per kg per hr), secretory volume rose to a steady state level of 32.5 +/- 10.2 ml per min. When a bolus injection of furosemide (20 mg) was given during continuous secretin infusion, mean secretory volume increased further to a maximum value of 110 +/- 14.7 ml per min. Similarly, the outputs of bicarbonate, sodium, and chloride increased significantly after furosemide, compared to values obtained with secretin infusion alone. Total bilirubin output fell after furosemide, suggesting that the effect of furosemide on secretory volume and electrolyte output was not due to a stimulatory effect on bile flow. Furosemide also had no effect on duodenal water transport. These observations demonstrate that furosemide stimulates pancreatic secretion of water and electrolytes, possibly via inhibition of pancreatic ductal absorption of sodium.