A simple reversed phase high-performance liquid chromatography (HPLC) method was developed for determination of celecoxib levels in human plasma. The procedure involves solid-phase extraction of celecoxib and the internal standard (SC-236) from plasma using C(18) extraction cartridges. The chromatographic separation of celecoxib and SC-236 was achieved with a Nova Pak C(8) column (3.8 mm x 150 mm) eluted with a mobile phase consisting of acetonitrile-tetrahydrofuran-sodium acetate buffer (pH 5.0) in the ratio of 30:8:62. An ultraviolet light detector with the wavelength set at 215 nm was employed for detection. Celecoxib was well resolved from the plasma constituents and the internal standard. The extraction recovery of celecoxib and SC-236 from human plasma was greater than 88%. Linear calibration curves were established over a concentration range of 40-4000 ng/ml when 0.25 ml aliquots of plasma were used. The inter- and intra-day R.S.D. for the assay was less than 12 and 5%, respectively. This assay has been applied to the analysis of celecoxib levels in plasma samples collected from healthy participants entered into a Phase II clinical study.