Seven patients with respiratory symptoms after welding were examined. Five had occupational asthma caused by fumes from manual metal are stainless steel welding. The detailed clinical results of two patients with repeated challenge tests are reported. One patient was nonatopic and had earlier had contact dermatitis due to chromium. He experienced a non-immediate type of asthmatic reaction after welding stainless steel. The other patient was atopic and showed an immediate-type reaction. Both reactions were repeated in the second provocation test after about 2 years. In addition both disodium cromoglycate and beclomethasone pretreatments inhibited the reaction of the two patients, but a placebo medication did not. A remarkable amount of chromium and nickel are detected in the fumes released during stainless steel welding but not in the fumes from mild steel welding, with which all provocation tests were negative. The chromium or the nickel in welding fumes might be the aetiological factor of the reaction.