We determined the apparent bioavailability of dicloxacillin in 26 children between the ages of 0.24 and 143 months by comparing the area under the serum concentration versus time curve following intravenous and oral administration of 25 mg/kg. With intravenous infusion the overall mean half-life of elimination was 0.53 ± 0.20 h, the AUC was 70.15 ± 32.18 mg·min/l and the apparent volume of distribution was 0.29 ± 0.09 l/kg. The overall average bioavailability was 59.89%. Children less than 6 months old had a shorter time to peak concentration (1.39 ± 0.49 h) and the lowest oral bioavailability (64.35± 13.62%) in comparison to children more than 60 months old. In children older than 60 months the time to peak was 1.79 ± 1.16 h and the average oral bioavailability was 79.38 ±32.87%. However, children less than 6 months old had the least variability in absorption, the coefficient of variation (CV) of oral bioavailability was 13.62%, while in children between 6 and 40 months old the CV was 60.4%: children older than 60 months had the most variability in absorption, a CV of 32.87%. This variability was not dependent on the formulation administered. After 5 years of age the bioavailability increased with increasing age.