We report five cases of asthma unmasked by anti-tumor necrosis factor (TNF)-α-blocking drugs. Asthma symptoms appeared within an average of 4 months (range 1-24 months) after starting the anti-TNF-α treatment for inflammatory disease. The patients did not appear to be predisposed to asthma except for one patient who had asthma during childhood. Four patients stopped anti-TNF-α-blocking drugs with an improvement of symptoms within 1 to 5 months. In the patient with a history of childhood asthma, respiratory symptoms recurred when another anti-TNF-α therapy was started. Asthma control was achieved with inhaled steroids, allowing anti-TNF-α treatment to continue. The biotherapy was maintained for the fifth patient in association with inhaled steroids. The pathophysiologic mechanisms are unknown but are probably more complex than the T helper 1/ T helper 2 imbalance suggested in the literature, and further studies are required.