Estradiol-17 beta-(beta-D-glucuronide) (E217G) was shown to be cholestatic in the isolated perfused female rat liver. Doses of 0.85, 1.3, 1.7 and 2.1 mumol decreased bile flow maximally at 15 to 30 min by 29, 37, 68 and 76% respectively. Approximately 95% of a dose of [3H]E217G was cleared from the perfusate in 30 min and was secreted in bile, with 93, 85, 71 and 55% of the dose appearing in bile within 120 min after doses of 0.85, 1.3, 1.7 and 2.1 mumol, respectively. Neither vehicle nor 1.7 mumol of estradiol-3-(beta-D-glucuronide) (E23G) significantly altered bile flow. Infusion of taurocholate at 40 and 60 mumol/hr, respectively, partially and completely protected against the cholestasis induced by 1.7 mumol of E217G. The log dose-response curve for E217G-induced cholestasis was much steeper and was shifted to the right in the presence of a 60 mumol/hr infusion of taurocholate. Infusion of taurocholate at 80 mumol/hr in the absence of E217G or E23G decreased bile flow by 79%. However, addition of 1.7 mumol of either E217G or E23G offered marked protection against taurocholate-induced cholestasis and increased bile acid secretion. Higher doses (3.4 mumol) of E217G or E23G further increased bile flow and bile acid secretion. A model system is presented to explain the mutual protection against cholestasis.