Patients with malignant disease are known to have an increased incidence of multinucleation in their tracheobronchial ciliated epithelial cells as compared with controls matched by age, sex and smoking habit. A seasonal relationship of viral inclusion bodies in the cilated epithelium of asymptomatic subjects has also been shown and is not related to age, sex and smoking habit. We have conducted an epidemiologic study to determine the possible relationships between these factors. Smears from 4,150 patients with a wide variety of pathologic conditions were examined for the presence of viral inclusions and multinucleated, ciliated epithelial cells. High degress of multinucleation were observed least frequenctly in the summer both in patients with and without known malignancy. Cytoplasmic inclusion bodies were also seen least frequently in the summer and autumn both in patients with and without know malignancy. In the presence of cancer, multinucleated epithelial cells and inclusion bodies were seen more frequently regardless of the season. When the seasonal incidence of multinucleated cells in 155 smears containing viral inclusion bodies was analyzed, it was found that patients without cancer had the lowest levels of multinucleation in the summer, whereas cancer patients had a depressed incidence of multinucleation in the winter and spring. Respiratory viruses may have a specific effect on the ciliated epithelium of cancer patients.