Human nasal epithelial cells, dissociated from nasal polyps, lost all their cilia when cultured as monolayers on 0.2% collagen gels in Ham's F12-DME 1/1, supplemented with NU-serum 10%, choleratoxin (10 ng/ml), retinoic acid (10(7) M) and antibiotics. These deciliated epithelial cell sheaths were then placed in a suspension culture system, and epithelial aggregates and vesicles formed. After 1 week in suspension, cilia progressively reappeared. This in vitro ciliogenesis resulted in ultrastructurally normal cilia with an intercellularly coordinated beating pattern. These epithelial aggregates and vesicles maintained this differentiated ciliary morphology and function for more than 6 months.