Nineteen nasal polyps from 13 patients were examined histologically. Nine polyps from seven cystic fibrosis (CF) patients could be positively identified by a triad of observations: delicate, barely visible basement membrane of surface epithelium without submucosal hyalinization, lack of extensive infiltration of eosinophils (Giemsa stains), and a preponderance of acid mucin in glands and cysts of the polyp and in its surface mucous blanket (Alcian Blue-periodic acid-Schiff stains). Two polyps from two patients with CF and atopy showed the characteristic findings of CF without modification. Eight polyps from four atopic patients without CF were identified by the reverse triad of changes: extensive thickening of the epithelial basement membrane and its extension into the submucosa as an irregular hyaline membrane, high stromal eosinophil count, and mainly neutral mucin in mucous glands, cysts, and mucous blanket. Hyperplastic mucous glands, mucous cysts of variable sizes, focal metaplasia of surface epithelium, and acid mucin in goblet cells were considered nonspecific lesions.