ABSTRACTMass‐examination of all 31 employees of a chemical factory revealed that 20 of them were proved or suspected to have contact hypersensitivities to chemical substances used in the factory as follows: 12 cases were sensitive to 2‐amino‐4‐chlorophenol, 5 to para‐aminophenol, 2 to para‐dichloronitrobenzene, and 1 to para‐nitrophenol. Among the 5 compounds tested (including the above 4 substances and 3′‐chlorodiphenylamine‐2‐carboxylic acid), 2‐amino‐4‐chlorophenol was found to be an e