A rapid, simple and sensitive assay was developed for determination of captopril in human serum. We employed silica gel cartridge for efficient extraction of captopril adduct from human serum. Captopril was trapped with p-bromophenacyl bromide (pBPB) to give captopril-pBPB adduct. A 4-ml benzene extract of 1 ml acidified serum was passed through 1 ml silica gel cartridge. Potential interfering compounds were removed with 4-ml benzene wash. The captopril-pBPB adduct was eluted with 0.5 ml acetonitrile. Of this acetonitrile solution (100 microliters) was injected on an ODS reverse phase HPLC column (chromatography conditions; mobile phase; acetonitrile-water-acetic acid (225:270:5, v/v/v), flow rate; 1 ml min-1, detection; UV at 263 nm). It is found that this method is accurate and does not require time consuming evaporation-concentration steps. Recovery exceeds 94% and analytical responses are linear over captopril concentration range from 50 up to 1000 ng ml-1. The coefficients of variation from 108 ng ml-1 to 605 ng ml-1 varied between 3.7-7.7% and the relative error did not exceed 3.7%. Therefore, this method can be used for routine clinical monitoring and in pharmacokinetic studies of captopril.