The bioavailability of cloxacillin and flucloxacillin were compared after the oral administration, in capsule form, of 500 mg cloxacillin or 250 mg flucloxacillin to healthy volunteers. There were no significant differences observed in time to peak concentrations, peak concentrations or area under the serum concentration/time curve. However, flucloxacillin had a significantly longer serum elimination half-life. Serum levels of cloxacillin and flucloxacillin were determined using a high-performance liquid chromatographic assay.