From the winter of 1997 to the spring of 1988, a severe epidemic caused by influenza A (H3N2) developed in Japan. During the epidemic (December 1997 to February 1998), 239 children were admitted to the pediatric ward of Nippon Kokan Hospital: as many as 76 (31.8%) were hospitalized with influenza A (H3N2) infection. Most were young healthy children (mean age, 3.7 years), suggesting the need of influenza immunization for this age group. 110 specimens of hospitalized children were examined by rapid antigen test of influenza A virus (Directigen Flu A, Becton Dickinson, USA). The rapid test showed about 90% sensitivity and specificity, as compared with isolation and serum hemagglutination inhibition test. Directigen Flu A proved to be a reliable, rapid screen for influenza A from symptomatic patients.