We report a case of occupational asthma and rhinitis caused by inhalation of 1,2-benzisothiazolin-3-one, an additive used as a microbicidal in detergent production, in a 26-year-old man employed in a chemical factory producing detergents. The subject's task consisted of pouring raw materials into the recipient of a machine which mixed the substances. Two months after the beginning of this job the patient complained of rhinitis and asthma at the workplace. The specific challenge test with 1,2-benzisothiazolin-3-one, one of the raw materials to which the subject was exposed, provoked an immediate prolonged asthmatic response and nasal symptoms, whereas exposure to other agents (e.g., alpha-amylase, alcalase or bezalkonium chloride) to which the patient was also exposed at work did not. To our knowledge this is the first case of occupational asthma and rhinitis caused by this compound.