Twelve asthmatic children (ages four to ten years) had attacks of asthma associated with influenza infection during the spring of 1985. Virus isolation and serologic studies proved eight cases were A/Philippine/2/82 (H1N2) and four cases were B/USSR/100/83. Four cases of A/Philippine/2/82 and two cases of B/USSR/100/83 were isolated from six control subjects who had suffered from influenza infection without asthma attack. The absolute lymphocyte count, T cell subsets increased in influenza patients both with and without asthma attack. However, the OKT4/OKT8 ratio markedly decreased in the influenza with asthma group during the acute phase. Since the fresh asthmatic patients had decreased OKT4/OKT8 ratio and increased lympho-proliferative response, IL-2 production increased after their lymphocytes were stimulated with housedust antigen and returned to near normal after hyposensitization therapy. Therefore, these results suggest that influenza virus has asthmagenicity and may contribute to precipitating an asthma attack.