Maximal blood concentration (Cmax), time to concentration peak (Tmax), area under the serum concentration-time curve (AUC infinity) and half-life (t1/2) after the oral administration of zopiclone 7.5 mg were compared in patients with severe renal failure (group I), with moderate renal insufficiency (group II), and in healthy volunteers (group III) over a 72-h period. Cmax did not differ from one group to the other but Tmax was significantly longer in group II. Half-lives were longer in renal patients than in healthy volunteers and AUC infinity s tended to increase with the degree of renal failure. Hemodialysis of the severely ill renal patients did not increase the plasma clearance of zopiclone. Finally, only small amounts of drug were found in urine in the three groups. Overall, results allow the conclusion that zopiclone may be safely used in patients with various degrees of renal impairment.