1. The turnover of deoxycholic acid and chenodeoxycholic acid was studied in six normolipaemic patients after oral administration of trace amounts of isotopically labelled compounds. 2. The mean values for half-life, pool size and turnover of deoxycholic acid were 3·0 days, 663 mg and 171 mg/day respectively. The corresponding values recorded for chenodeoxycholic acid were 2·8 days, 781 mg and 207 mg/day. 3. A comparison of the turnover rates of deoxycholic acid and cholic acid in three subjects indicated that 25–61% of the cholic acid was converted into deoxycholic acid. 4. Only trace amounts of radioactivity were recovered in the trihydroxycholanic acid fraction of duodenal bile after the administration of [14C]deoxycholic acid or [3H]chenodeoxycholic acid.