CT scans of eight nonsmoking patients with chronic sinusitis and two controls were graded for their disease severity (from 0 to IV) with the classification system proposed by May. Subsequently, endoscopically harvested middle turbinate specimens from these patients (16 diseased turbinates, 4 controls) were evaluated both by scanning and by transmission electron microscopy. As the severity of the disease increased as demonstrated by CT scan, electron microscopy of 5 x 3 x 0.05 mm mucosal specimens demonstrated that the number of ciliated cells decreased whereas the number of goblet and squamous cells increased. As the disease progressed to stages III and IV, scanning and transmission electron microscopy demonstrated areas of squamous metaplasia and areas completely denuded of epithelium. The increased goblet cell population, the loss of cilia and ciliated cells, and the patches of denuded epithelium may account for the recurrent bacterial infections and chronic nasal drainage seen in patients with chronic sinusitis. The extensive mucosal changes that occur in grade III and IV disease are similar to those occurring in cigarette smokers, and it takes years to recover after discontinuation of smoking. Delayed recovery of the mucosal epithelium may account for both the recurrent infections and the slower response to treatment on the part of patients with extensive grade III and IV changes on the CT scan.