1. A modification of the competitive protein binding assay for prednisolone described by English, Chakraborty & Marks (1974) is presented. 2. Addition of pg quantities of [3H]‐prednisolone following oral dosage with prednisone or prednisolone. 3. Mean plasma half‐life and peak plasma concentrations in patients with respiratory disease seen following prednisolone administration agree well with previous studies in healthy volunteers performed by other workers using competitive protein binding and radioimmunoassay techniques. 4. A considerable inter‐patient variation in bioavailability after a standard dose of prednisolone (20 mg) was noted.

1 Ephedrine plasma levels have been measured in ten asthmatic patients given a singel dose of ephedrine hydrochloride (22 mg) along and in combination with theophylline and a barbiturate. 2 Pharmacokinetic assessment of the data indicated no significant intra‐subject changes in kinetic parameters before or after chronic treatment with ephedrine HCl (11 mg three times a day) alone or in combination. 3 Tolerance to these therapeutic doses, if it occurs, is therefore not disposition‐ related but rather to pharmacodynamic changes.