Persulphate salts, which are common constituents of hair bleaches, have occasionally been reported to cause occupational asthma in hairdressers. We describe the clinical and immunological studies carried out in a hairdresser who developed cutaneous and respiratory symptoms, about 1 year after being employed in a hairdressing salon. Skin prick tests with 1:5 w/v potassium and sodium persulphate extracts were positive in our patient at 15 min and negative in control subjects. The European standard contactans (ECDRG) and a battery of hairdressing agents were patch tested with positive result to KATHON CG (isothiazolinone). The methacholine-inhalation test showed airway hyperresponsiveness. Bronchial provocation test with a 1:50 w/v potassium persulphate extract elicited a nonimmediate asthmatic reaction, followed by recurrent nocturnal fall in FEV1 lasting up to 3 days after the test. Plethysmography results revealed air trapping caused by a marked increase of airway resistance 3 h after the specific bronchial challenge. Histamine release test was not conclusive, and the determinations of specific IgA, IgM, IgG and IgG subclasses by EIA and IgE by RAST against persulphate salts were negative.