Abstract: Occupational contact dermatitis occurred during the production of the dye Cationic Brilliant Yellow 7GL came to the highest incidence among the dye-workers in Shanghai. The.prevalence rate of the workers through clinical investigation was 39.32%, while the incidence through retrospective study was 30.77%. The occurrence of the dermatitis was closely related to the intermediate 2-dichloro-methyl benzimidazole which was, further confirmed to have a strong sensitizing potential. The positive reaction rates were 57.14% and 59.09% in patch test and in GPMT respectively. Preliminary effect preventive measures achieved a marked.