We assessed whether patients with decompensated congestive heart failure had altered absorption of oral furosemide. Pharmacokinetic and pharmacodynamic responses were studied in 11 patients receiving their usual oral dose of furosemide while decompensated, and after attaining normal weight. Seven patients also received 25 g of oral D-xylose to further assess intestinal absorption. A 57% decrease in lag time (p = 0.033), a 27% decrease in time to peak serum concentration (p = 0.041), and a 29% increase in the peak serum furosemide concentration (p = 0.008) were seen in compensated as compared to decompensated patients. No significant change was seen in absorption or elimination half-lives, area under the serum concentration versus time curves for furosemide, or in absorption of D-xylose. Although the pharmacodynamics of furosemide were reduced compared to normal subjects, there was little difference in the compensated and decompensated states. Our results show an alteration in furosemide absorption in decompensated congestive heart failure.