We assessed the handling of and response to oral bumetanide (1.0 and 2.0 mg) and to furosemide (40 and 80 mg) in 20 patients with stable, compensated congestive heart failure (CHF), comparing the two drugs and, in addition, examining differences from normal subjects. Bumetanide and furosemide were similar in time course of absorption, but patients with CHF had considerably prolonged absorption compared to normal subjects causing attainment of lower peak concentrations of drug. In both CHF and normal subjects, more bumetanide than furosemide was absorbed. The elimination half-life of furosemide was approximately twice that of bumetanide, and both were about two times longer than respective values in normal subjects. "Dose"-response curves were shifted downward from normal with both drugs. In patients with CHF, overall response did not differ between bumetanide and furosemide. The two drugs exhibit subtle differences, the clinical importance of which appears to be negligible from this study. Importantly, however, both drugs showed delayed absorption causing attainment of peak urinary excretion rates of diuretic two- to threefold lower than in normal subjects. This effect along with the abnormal responsivity of the tubule may contribute to the "resistance" to oral doses of diuretics observed clinically even though no quantitative malabsorption of drug occurs.