In a clinical study involving 22 normal adult volunteers, the bioavailability and pharmacokinetics of prednisone tablets with varying dissolution rates were evaluated. Serum levels were measured by a radioimmunoassay for prednisolone. Absorption rate constants and serum half-lives are presented. Substantial serum levels of prednisolone were attained quite rapidly (within 0.5 hr). The observed serum levels were statistically analyzed and fitted to the one-compartment open model with first-order absorption and elimination. A qualitative correlation between the in vitro dissolution rate and the calculated initial absorption rate constants was found. However, the in vitro dissolution rates were not predictive of the overall bioavailability of the prednisone tablets tested in terms of peak concentration and area under the serum concentration-time curve.