The prevalence of positive skin-prick test reactions ammonium persulphate and potassium persulphate (1% and 5% solutions) was tested in a cross-sectional study on 52 employees of a company producing persulphates after a case of "persulphate asthma" was observed. A random test of 13 persons without occupational exposure to persulphates served as controls; among them all the skin-prick test reactions were negative. Eight company employees showed a positive skin-prick test reaction to at least one of the persulphate solutions tested. Employees showed lower lung function results with a positive prick test reaction than did employees with a negative result. The positive skin-prick reactions correspond well to the anamnestic data and indicate a possible relationship to obstructive ventilation disorders. The results therefore suggest an IgE-induced, allergic pathomechanism of "persulphate asthma" triggered by persulphates.