Abstract To assess the effect of specific immunotherapy (IT) on the immediate and late asthmatic responses induced by cat or dog extract bronchial provocation testing, we studied seven cat-sensitive and six dog-sensitive subjects with asthma. Among the cat-sensitive subjects, two of three subjects displaying only an immediate asthmatic response before IT lost the response after 3 months of IT with cat extract, whereas only one of four subjects with the dual (immediate and late) asthmatic responses had ablation of such responses (no significance for the one-tailed test). Three subjects had worsening of the immediate response after IT. Among dog-sensitive subjects with asthma, three of five subjects with only an immediate response demonstrated an ablation of the immediate response, whereas the one subject who was the only subject with a dual response before IT lost the dual response after dog-extract IT ( p value of 0.005 on one-tailed test). Immediate systemic side effects, including one episode of anaphylaxis, occurred on seven occasions of 326 injections with cat extract compared to only one episode of rhinitis of 289 injections with dog extract.