Two workers developed dermatitis, rhinitis, bronchitis, and asthma after occupational exposure to dusts of persulfate salts. The causative role of the persulfate salts could be confirmed by case history, skin tests, occupational exposure tests and by removal of the 2 workers from their jobs. Patch tests produced late cutaneous reactions. Occupational exposure at the working place for 8 h resulted in each case in a pathological increase of airway resistance. Withdrawal from occupational exposure to persulfate salts resulted in recovery within a few days. Our results suggest that chemically irritative or toxic effects of persulfate salts play the predominant role in the pathogenesis of the reported cases.