To study the pharmacokinetics of single increasing intravenous doses (40-160 mg) and repeated doses (80 mg for 7 days) of lecithinized superoxide dismutase (PC-SOD) in Japanese volunteers and to compare the pharmacokinetics of PC-SOD between Caucasians and Japanese. The Japanese study consisted of 2 parts: a single-dose, open-label, dose-escalation part and a multiple-dose, single-blind, placebo-controlled part. The pharmacokinetics of PC-SOD were determined using noncompartmental and compartmental methods. Pharmacokinetic data from a study with PC-SOD in Caucasians were reanalyzed using the same methodology. The mean (SD) terminal half-life of PC-SOD in Japanese subjects was 25 (4) hours for the 40-mg and 80-mg doses and 31 (15) hours for the 160-mg dose. There was nonlinearity between dose-normalized C(max) and clearance (P values .002 and .022). After multiple dosing, steady state was reached after 5 days. The observed accumulation ratio was 2.6 (0.5). The pharmacokinetics of the single 80-mg dose were similar for Japanese and Caucasians. The pharmacokinetics of PC-SOD was shown to be nonlinear with dose, which may be attributable to a saturable clearing mechanism. The relatively long half-life of PC-SOD (>24 hours) suggests that it is worthwhile to study the compound as a protective agent in clinical conditions with free radical overload.