The biliary elimination of ceftriaxone was studied by an isolated perfused rabbit liver model (n = 5). After adding of 10 mg of this antibiotic to the circulating blood of this preparation, a mean biliary peak level reaching 120.5 +/- 24.6 micrograms/ml was obtained between the 30th and 60th minutes. The total amount of ceftriaxone eliminated unchanged in the bile collected during a 3h period represents 8.8 +/- 2.6% of the administered dose. At the end of this study period, 32.7 +/- 3.3% of the initial dose remained in the circulating blood. The hepatic tissue concentrated 3.7% of the whole dose. At last, control experiments proved that 36.4% of the added antibiotic has been degraded by the experimental system itself. Thus the remaining 18.4% can be attributed to a hepatic biotransformation of ceftriaxone.