1 Doses of 16, 32, 48 and 64 mg prednisolone were administered intravenously to normal volunteers who also received 100 prednisolone orally. Plasma prednisolone concentrations were estimated by quantitative thin layer chromatography. 2 The bioavailability fraction was 1.063 +/- 0.154 (s.d.) indicating complete availability of prednisolone following oral administration. 3 The mean T 1/2 over all doses were 4.11 +/- 0.97 (s.d.) h and there was no evidence of a dose-related change in its value. 4 The mean systemic clearance over all doses was 0.104 +/- 0.034 (s.d) 1 h-1 kg-1. There was no evidence of a dose-related change in clearance or in the apparent volume of distribution (overall mean 0.588 +/- 0.152 1 kg-1). 5 The area under the plasma concentration-time curve was linearly related to dose. 6 Plasma concentration-time curves normalised for dose were superimposable. 7 It was concluded that over the dose range investigated, non-linear pharmacokinetic behaviour had not been demonstrated in this group of normal volunteers.