1 In a pharmacokinetic study in six volunteers serum fusidic acid concentrations were obtained after rapid intravenous administration of 100 mg. 2 Analysis of the data suggests that the serum concentration/time curve is biphasic and that the curve can be described by the following equation: cp=5.9e(-1.82t)+4.3e(-0.13t). 3 The disposition characteristics of sodium fusidate have been calculated from this relationship and a plasma half life for sodium fusidate of between 5 and 6 h obtained. 4 Subsequently plasma fusidic acid levels have been measured in the same volunteers on three occasions after sodium fusidate (500 mg) given either as a slow intravenous infusion, or orally as a capsule or as a suspension. 5 Serum levels and AUC after a capsule were about 75% of those obtained after the infusion (30 and 70 mg/1 at peak respectively) whereas levels and AUC after the suspension were only about 50%.