The extent to which debrisoquine (D) is metabolized to 4-hydroxydebrisoquine (4OHD) was found to be influenced by the ethnic origin of the subjects. Following ingestion of 20 mg of debrisoquine sulfate, Orientals excreted, on the average, significantly more D and less 4OHD in 0- to 8-h urine than Caucasians; however, the sums of D + 4OHD did not differ.