The pharmacokinetics of quinine after a single 600 mg oral dose of quinine sulphate were studied in seven female subjects who used oral contraceptives and in seven age-matched female controls who did not. There were no significant differences (P > 0.05) in the maximum plasma concentration (Cmax) and the time of peak concentration (tmax) between the subjects who used oral contraceptives (Cmax = 5.3 ± 1.0 (s.d.) mg l-1; tmax = 1.4 ± 0.7 h) and the control subjects (Cmax = 5.6 ± 0.9 mg 11; tmax = 2.1 ± 0.9 h). The mean elimination half-life of quinine in the oral contraceptives user group (12.5 ± 1.9 h) was similar (P > 0.05) to that in the control group (11.8 ± 2.7 h). The oral clearance of quinine in the oral contraceptive user group was 0.133 ± 0.055 1 h-1 kg-1 (range 0.073-0.233) and was not significantly different (P > 0.05) from that observed in the control group (0.125 ± 0.025 1 h-1 kg-', range 0.075-0.148).