OBJECTIVE: To study the pharmacokinetics and relative bioavailability of clarithromycin capsule. METHODS: A microbiological agar diffusion assay using Micrococcus luteus(ATCC 28001) was used as a bioassay for clarithromycin in serum following a single oral dose 500 mg of clarithromycin capsule and tablet respectively given to 10 healthy volunteers in an open randomized crossover test.The data obtained were fitted with PKBP-N1 program. RESULTS: A linear relationship was obtained between the peak area ratio and the concentration of clarithromycin from 0.05 to 4.00 μg·ml_-1and the lowest limit of detection of clarithromycin in serum was 0.05 μg·ml_-1Precisions were under 8.20%.The recoveries were 99.04%～101.48%.The onecompartment open model with first order absorption was used to described the time course of serum concentrations of clarithromycin in human following administration of a single oral dose 500 mg as capsule and tablet.The results were t_peak=(1.45±0.50) h and (1.55±0.44) h,c_max=(2.20±0.39) μg·ml_-1and (2.15±0.33) μg·ml_-1,AUC=(17.60±2.85) μg·h·ml_-1 and (17.74±3.46) μg·h·ml_-1. CONCLUSION: There were no significant differneces between their pharmacokinetic parameters.The tested capsule and the reference tablet is bioequivalent with F_rel=101.64%.