In the hope of warning those who work with iodoacetic acid, we report 2 cases of dermatitis due to contact with this reagent. In the recent past, there has been considerable increase in the use of this acid in medical laboratories where the Huggins-Miller-Jensen (HMJ) test1is being investigated. Iodoacetic acid is a derivative of acetic acid in which one hydrogen atom is replaced by an iodine atom. In the purified state the acid is a white crystalline substance, molecular weight 185.94, with a melting point of 82 C. Chemically, it is generically related to the chlorine-substituted acetic acids, which are corrosive substances popularly used today for the removal of certain superficial skin lesions. It is necessary for laboratory personnel to handle iodoacetic acid daily in connection with the performance of the test. Some of the iodoacetic acid available today must be recrystallized to obtain the necessary purity, and,