Three laboratories participated in the interlaboratory study of an enzyme immunoassay (EIA) method for determination of sulfamethoxazole (SMX) using samples of the same muscle, liver and plasma from chickens administered with SMX. Interlaboratory variation in the determined values were similar to those of other studies determined by gas chromatography and liquid chromatography. It was suggested that the interlaboratory difference in determined SMX residues from chicken tissues did not become problems of using EIA method, in spite of the differences of equipments and operators.