A duodenal perfusion technique which permitted a normal daytime eating pattern of three liquid meals and an overnight fast was used to measure the 24-hr output of copper in bile in 19 studies in 14 persons with normal hepatic and gallbladder function. Daily biliary output was also determined by direct measurement on four 24-hr bile collections obtained from 3 patients with complete biliary diversion, and in 4 patients measurements of dietary copper intake and fecal copper output were also made. A mean bile copper output of 25 +/- 13 microng per kg-day (1.7 mg +/- 0.8) (mean +/- SD) was obtained in 19 perfusion studies; the range was 9.0 to 53.0 microng per kg-day. The values in the 24-hr bile collections were similiar to those obtained using the perfusion method. Biliary copper output was similar during the day and night, and there was no correlation between hourly rates of copper output and hourly rates of bile acid output, nor was there any correlation between daily copper output and daily bile acid output. The similar values for dietary intake, biliary output, and fecal output provide additional support for the current view that in healthy man copper balance is maintained by biliary secretion and subsequent fecal excretion of copper which has been absorbed in the stomach and proximal duodenum.