The pharmacokinetics of ciprofloxacin after a single 500 mg oral dose was studied in one group of healthy volunteers and in patients affected by liver cirrhosis and classified into three groups according to Child-Turcotte criteria. The serum concentrations were determined by an agar well diffusion assay 0.5, 1, 3, 6, 12 and 24 h after the administration of the drug. No significant differences were noticed in Cmax, Tmax, T1/2 and AUCtot in the group A and B of patients and in the control group. Class C patients showed on the other hand a Cmax 15-25% higher than in other groups (2.74 mcg/ml), a T1/2 1.12-1.42 hours longer than in other groups and a consequent much higher AUCtot (17.70 mcg/h/ml). The concomitant administration of diuretics of anti-H2 drugs was also evaluated as possible factors affecting the ciprofloxacin pharmacokinetics, but no significant differences were noticed. A mild or moderate impairment of the liver function did not affect the pharmacokinetics of ciprofloxacin, but the severe impairment of the liver function could affect its Cmax and serum half-life, so that further studies with multiple doses will be needed to evaluate if any dosage adjustment would be required in these patients.