A high-performance liquid chromatographic method for the determination of the theophylline solubilizer salicylamide-O-acetic acid has been developed in the range 0.5 to 10 microg/ml for human serum and 5 to 400 microg/ml for urine. Reversed-phase ion-pair chromatography was employed with tetrabutylammonium hydrogen sulphate as counterion and 2-nitrophenylacetic acid as internal standard. Preliminary pharmacokinetic single-dose studies show that the sensitivity and the selectivity of the assay are adequate to measure lower concentrations in the late beta-phase.