A fluorometric high-performance liquid-chromatographic method is described for the determination of cyanate in human plasma. The method is based on the derivatization of cyanate with 2-aminobenzoic acid (anthranilic acid), leading to a stable cyclic fluorescent product, 2,4(1H,3H)-quinazolinedione. The fluorescent product was extracted with ethyl acetate, passed through a cation-exchange resin to eliminate the excess of derivatization reagent, and then concentrated on a Sep-Pak C-18 cartridge before reversed-phase chromatography and fluorometric detection. The precision of the method was satisfactory (coefficient of variation 2.3%) and the analytical recovery was quantitative (103%). Detection limit was found to be 8 nmol/liter from a 1-ml plasma sample. Cyanate in plasma was stable for 3 months when stored in liquid nitrogen. The mean and SD cyanate level in human plasma from 17 healthy nonsmoking subjects was 45 +/- 21 nmol/liter.