To assess the relative bioavailability of a recently developed liquid prednisone preparation, prednisolone pharmacokinetics were evaluated after the administration of three separate steroid preparations. On 3 study days, each 2 wk apart, 12 healthy subjects received in random order: prednisone liquid, prednisone tablet, and prednisolone sodium phosphate. Plasma samples were collected over a 12 hr study period and analyzed for prednisolone concentration by high-pressure liquid chromatography. Tablet data demonstrated a time-to-peak concentration of 1.23 +/- 0.68 hr (SD), mean residence time of 5.1 +/- 0.49 hr, and absolute bioavailability (tablet/i.v.) of 97.5% +/-- 17.5%. Liquid data demonstrated a significantly (p less than 0.01) shorter time-to-peak concentration, 0.54 +/- 0.20 hr, and mean residence time 4.6 +/- 0.34 hr, with no significant difference in absolute bioavailability (liquid/i.v.), 88.2% +/- 15.8%. This resulted in significantly (p less than 0.05) higher plasma prednisolone concentrations for the liquid preparation in the first 0.75 hr and significantly lower concentrations after 1.5 hr as compared with the tablet. Prednisolone area under the plasma concentration vs time curve for the liquid prednisone formulation was 90.0% +/- 13.2% of the tablet preparation. Thus prednisone liquid has comparable bioavailability to the tablet, with an earlier peak plasma prednisolone concentration and significantly higher plasma prednisolone concentrations within the first hour of administration.