Dissociated human nasal epithelial cells from nasal polyps were cultured in Ham's F12-DME 1/1 supplemented with NU-serum 10%, choleratoxin (10 ng/ml), retinoic acid (10(-7) M) and antibiotics. In monolayer cultures, the epithelial cells grew to confluency on collagen gels, became squamous, and lost their cilia within 2-6 weeks. In suspension cultures, epithelial cell sheaths formed stable vesicles and aggregates. These maintained a respiratory-type morphology and normal ciliary activity for over 6 months. When deciliated, squamous cells from monolayer cultures were brought in suspension, a respiratory-type morphology with cilia reappeared. This in vitro ciliogenesis resulted in normal and coordinated ciliary activity observed for more than 5 months.