Allergic contact dermatitis due to a biocide containing 5-chloro-2-methyl-4-isothiazolin-3-one

3 cases of contact allergy due to the biocides 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one are reported. 2 workers exposed to a soluble oil containing these 2 biocides experienced allergic contact dermatitis from them. The 3rd case was that of the chemist who separated the 2 materials for the execution of this investigation. These compounds are chemically related to the biologically active components of Ectimar, Skane M-8 and Proxel CRL. Further instances of contact allergy due to these and related compounds are likely because of the apparently increasing use of such substances as antimicrobial agents in various commercial products.