The urinary excretion of a 0.75-mg oral dose of digoxin was assessed in 8 healthy men during a control 5-day period and then, after a washout period of at least 2 wk, during a 5-day period when the subjects also took oral furosemide, 40 mg daily. Analysis of the raw data by a paired Student's test and analysis of variance of log-transformed urinary digoxin excretion data revealed no significant difference attributable to the addition of furosemide (F = 1.16; df = 1,21). The treatment by day interaction showed the slopes to be consistent between the two treatments. It seems that in the presence of normal renal function there is no need to alter loading or maintenance doses of digoxin when furosemide is also given. Analysis of variance with log transformation of data is suggested as a practical approach to handling digoxin urinary excretion results when the transformation linearizes the data through examination by the method of orthogonal polynomials.