OBJECTIVE Zidovudine is often administered every 12 h in HIV-infected children, but so far no pharmacokinetic data are available for the administration of this agent every 12 h. We have evaluated the plasma pharmacokinetics of zidovudine administered every 8 h versus every 12 h in HIV-1-infected children. METHODS In HIV-1-infected children who switched from zidovudine every 8 h to every 12 h, a pharmacokinetic curve was recorded both before and after the switch. Zidovudine plasma levels were measured by HPLC. Pharmacokinetic parameters were calculated by non-compartmental methods. RESULTS Six HIV-1-infected children [median age (range) 7.8 (2.5-13.4) years] were included. In these patients, geometric mean ratios of AUC(0-24) and C(max) for zidovudine every 12 h versus every 8 h were not significantly different from 1.0. CONCLUSIONS The plasma pharmacokinetic parameters of zidovudine taken every 8 h and every 12 h were not significantly different and therefore suggest bioequivalence of these two dose frequencies.