The pharmacokinetics of zidovudine (azidothymidine, AZT) was investigated after oral administration (200 mg) in 14 human immunodeficiency virus seronegative patients with liver cirrhosis. They were divided in three groups according to the severity of the liver disease quantitated by the Child-Pugh score. Plasma and urine concentrations of zidovudine and its glucuronidated metabolite (GAZT) were measured simultaneously by HPLC assay. Findings were compared with those previously measured in six healthy volunteers. As a consequence of a marked drop in oral clearance (10 +/- 4 versus 38 +/- 15 ml/min/kg), zidovudine concentrations, half-life, and mean residence time were increased in patients with cirrhosis. No difference could be established between the three groups. The reason for such a decrease in oral clearance of zidovudine was the reduction in the GAZT formation clearance (236 +/- 73 versus 1540 +/- 540 ml/min); this led to a decrease in the AUC ratio of GAZT and zidovudine (1.3 +/- 0.6 versus 4.6 +/- 0.7), which was directly related to the severity of the cirrhosis. In patients, as in volunteers, formation of GAZT rate limits its elimination. To avoid important cumulation of zidovudine after repeated dosing in patients with acquired immunodeficiency syndrome who have hepatic impairment, a dosage adjustment could be proposed.