We developed a new assay method for fluoride anion (F(-)) a specific metabolite of sarin. Trimethyifluorosilane (TMFS) was derivatized from F(-) with trimethylsilanol, and TMFS was detected with a GC-flame ionization detector (FID) and capillary column system. The linear range, detection limit and recovery rate were 0.02-10 ppm, 0. 01 ppm and 97.3-103.0%, respectively. The patients were reported to be exposed only once to the toxic substance (a bolus exposure). F(-) excretion in urine of the hospitalized patients demonstrated three or four peaks. Other common metabolites of sarin and by-products such as methylphosphonic acid (MPA) and isopropyl alcohol (IPA) also showed two or three peaks. These results suggested that the patients were exposed to not only sarin but also fluoride and isopropyl alcohol containing by-products. The sum of MPA excreted was 0.3-90 mM, far exceeding the human lethal dose of sarin. The residual acetyicholine esterase activity of erythrocytes on admission (4.7-57.2% of the individual reference value) of the patients showed statistically significant relationships only with the initial values of F(-) and the isopropyl methylphosphonate. This evidence also suggested the exposure to fluoride and isopropyl alcohol-containing by-products.