Eight asthmatics with respiratory intolerance to NSAIDs and two subjects (one asthmatic, one healthy) only sensitive (asthma) to pyrazolone drugs were challenged under single-blind conditions with a new NSAID, carprofen. No adverse effects were observed in patients sensitive to pyrazolones. Among the other patients, only three developed considerable bronchial obstruction which was rapidly reversed by inhalation of a beta 2-stimulant (fenoterol: 2 puffs). Two subjects developed nasal obstruction with rhinorrhoea: in conjunction with bronchoconstriction in one patient and alone in the other. In conclusion, acute administration of carprofen in patients with respiratory intolerance to NSAIDs, in contrast to most other NSAIDs, never creates a situation of real danger even though in some patients it may considerably increase nasal and bronchial resistance.