To evaluate,the differences of benzidine exposure patterns of the workers in two benzidine-based dye manufacturing factories, the concentration of benzidine: in. air, blood, and urine were measured. The air levels of benzidine dihydrochloride and benzidine-based dye were measured by high performance liquid chromatography with ultraviolet detector. Blood samples were collected at 3 hours after exposure and urine samples were collected at the end of shift. Blood and urine samples were analyzed by high performance liquid chromatography with electrochemical detector. The level of benzidine in reaction process (input, diazotization, and coupling); was 0.381+/-7950 g/m3. The blood benzidine was deteced in 25 workers among 38 in reaction process and their mean levels were 0.0153?0376 ng/mg Hb. The urinary benzidine was detected for 11 workers among 38 workers in the reaction process. The level of benzidine-based dye in drying and packing process was 52.1748+/-4.4111g/m3. The blood benzidine was deteced in 6 workers among 38 in drying and packing process and their mean levels was 0.0062+/-0274 ng/mg Hb. The urinary benzidine was detected for 1 worker among 38 workers exposed to benzidine-based dye. The blood and urinary benzidine were detected in workers exposed to benzidine-based dye. Such results suggested that some part of benzidine-based dye was metaboized to benzidine. Therefore, some regulations for manufacturing and use of the benzidine-based dye are needed to prevent its hazards in industries.