A cross-over, double-blind, randomized trial with 8 healthy volunteers was undertaken to compare prednisolone and prednisone pharmacokinetics after a single oral dose (1 mg/kg) of prednisone (Cortancyl) and prednisolone sodium metasulfobenzoate (Solupred). Maximum prednisolone concentrations measured after ingestion of prednisone are higher (535 +/- 32 ng/ml) and occur earlier than after taking prednisolone sodium metasulfobenzoate (198 +/- 114 ng/ml) (p less than 0.001). The areas under the curve are significantly larger after prednisone than after prednisolone sodium metasulfobenzoate (p less than 0.02). These findings suggest a decreased systemic availability of prednisolone after prednisolone sodium metasulfobenzoate (Solupred) administration and show, from a strictly pharmacokinetic point of view, that equimolar doses of prednisone and prednisolone sodium metasulfobenzoate are not equivalent therapies.