A new high-performance liquid chromatographic (HPLC) method has been developed for the determination of the cysteine prodrug, L-2-oxothiazolidine-4-carboxylic acid (Procysteine), in human plasma. Samples were mixed with 5% metaphosphoric acid and the supernatants chromatographed using a reversed-phase analytical column. Procysteine was detected spectrophotometrically at 230 nm and quantitated by comparison with a standard curve of known amounts of Procysteine (20-1000 microM) in plasma. The coefficients of variation for 48.6 microM and 676 microM control pools were 6.5 and 4.0% respectively (n = 46). Deviations from the expected concentrations were less than 2%. The method has been utilized to evaluate the pharmacokinetics of a wide range of oral and intravenous doses.