Sixteen workers, from a platinum refinery, with respiratory disease were tested with solutions of complex salts of platinum and ten gave immediate prick test reactions to concentrations of 10−4−10−6and immediate nasal reactions in seven out of eleven tested to concentrations of 103−10−8. Occupational-type exposure inhalation tests to the dust from mixtures of 40 mg of the platinum salt with 1 kg of lactose gave immediate asthmatic reactions in eight and in one of these a late reaction, all also giving immediate prick test reactions. The asthmatic reactions were inhibited by disodium cromoglycate. In two with negative prick tests, late asthmatic reactions were elicited. The occupational-type exposure test provides a safe, acceptable procedure for etiological diagnosis.