A 28 year old man with no history of atopy was referred to our hospital for possible work-related asthma. He had been employed in the production section of a pharmaceutical company for 2 yrs, and in the last 2 months he had complained of dyspnoea, wheezing, chest tightness, symptoms of rhinitis and a cutaneous rash when exposed to powdered antibiotics. Symptoms disappeared after being transferred to the packaging section. When the subject was admitted to our department he was asymptomatic. Basal lung function tests were in the normal range. Bronchial challenges with methacholine and with ultrasonically-nebulized distilled water were negative. Skin-prick test with piperacillin sodium gave a strong positive response at a very low concentration. Specific inhalation challenge with piperacillin sodium resulted in an immediate asthmatic reaction, and also reproduced rhinitis symptoms and the cutaneous rash. A control challenge with lactose, and the specific challenge test with cefuroxime sodium (another antibiotic to which the patient was exposed at the workplace) were negative. We conclude that piperacillin sodium is an agent that can cause occupational asthma.