There are considerable evidences that viral upper respiratory tract infection precedes the episodes of acute sinusitis. Yet the causal relationship between viral upper respiratory tract infection and sinusitis has not been established conclusively. It was been reported that damages of the ciliated epithelium and decreased mucociliary clearance play important roles in the development of acute sinusitis and influenza virus also has been reported to augment the adherence of microorganism to host cells and induce polymorphonuclear leukocyte dysfuncton. The purpose of this study was to determine the direct effects of viral infection on the mucosal epithelium, i.e., the histopathologic changes and effects on the adherence of Streptococcus pneumoniae to the sinus mucosa during the experimental influenza a virus-induced infection. Influenza a virus ; strain A/Korea/1/80(H3N2) was inoculated into the maxillary sinus of New Zealand white rabbits. Rabbits were examined histopathologically at different intervals up to 28 days after inoculation. Ciliated cells appeared to be the primary target and maximum damage was observed at the 7th day observation. Other prominent histopathologic findings were acute inflammatory cell infiltration capillary engorgement, subepithelial hemorrhage and tissue edema. Regeneration of cilia and ciliated cells started from 5 days after viral infection. Four weeks were required to restore the ciliated epithelium to normal. The adherence of Streptococcus pneumoniae on the sinus mucosa was significantly increased at 3rd(p<0.05) and 7th day(p<0.01) after inoculation compared with the control group. These results suggest that influenza virus infection may result in mucosal changes as well as increase the bacterial adherence, but it recovers without significant sequelae. Therefore, a careful observation for secondary bacterial infection would be necessary in early stage of viral infection.