Abnormal respiratory cells have been reported in cases of chronic pediatric respiratory infection. In some cases, there is a specific defect of most cilia, but in others there is a variety of derangements of the architecture of only a fraction of the cilia. Histologically normal lungs from two children without known respiratory disease were examined and found to contain many abnormal cilia of the polymorphic type, which accounted for 3% to 5% of all cilia. Abnormalities included (1) excess cytoplasmic matrix, (2) additions, deletions, or aberrant arrangements of the 9 + 2 tubular pattern, (3) multiple partial or complete cilia within one membrane, and (4) occasional marked disorganization of all cilia in a cell. Polymorphic ciliary abnormalities may be common in healthy children, and should be cautiously interpreted as a cause of chronic respiratory infection.