We compared the expression of intercellular adhesion molecule (ICAM)-1 and lymphocyte function-associated antigen (LFA)-1 alpha (alpha) on the surfaces of peripheral immunocompetent cells of young children infected with respiratory syncytial virus (RSV) and influenza virus. Flow cytometric analysis revealed a significantly higher percentage of CD14 + monocytes/macrophages that were strongly ICAM-1-positive in the influenza group than in age-matched controls, whereas the ICAM-1 expression levels of the RSV and control groups did not differ significantly. Analysis of LFA-1alpha expression by CD3 + T lymphocytes showed a significantly higher percentage of strongly positive cells in the influenza group than in the age-matched controls. By contrast, the percentage of cells that were strongly LFA-1alpha-positive was significantly lower in the RSV group than in the age-matched controls. These results suggest that no increase of adhesion molecule expression occurs in vivo in patients with RSV infection, and also that there is little activation of peripheral blood monocytes/macrophages and T lymphocytes in young children with RSV infection.