Epidemiologic study of 13 influenza A/New Jersey/76 (Hsw1N1) patients indicated that person-to-person transmission had occurred in several distinct military units. Soldiers in eight of these units (companies) were studied to determine whether they had experienced influenza A/New Jersey infections and associated acute respiratory disease. Titers of hemagglutination-inhibiting antibody to influenza A/Mayo Clinic/103/74 (Hsw1N1) antigen were determined. In seven of these eight companies, individuals with titers of ⩾1:20 were found. In these seven companies, members of platoons with cases (contact platoons) had antibody prevalences of 7%–56%, and members of platoons without cases had prevalances of 0–40%. Hospital admissions for acute respiratory disease were proportionately greater in trainees with A/Mayo Clinic antibody titers of ⩾1:20 than in trainees without antibody in five of six contact platoons studied.