Different in vitro culture systems have been used to study the functional properties of respiratory epithelium and to unlabel the pathogenesis of its dysfunction. They have some problems that dissociated epithelial cells cultured on plastic or collagen become extremely squamous and lose their cilia. Others have shown that reciliation takes place after suspension, floating or using air interface, even after paper is to establish floating method, an in vitro culture system, where human nasal epithelial cells can differentiate into ciliated cells and secretory cells simultaneously. Dissociated human nasal epithelial cells from nasal polyp were cultured in Ham's F12-dulbecco's modified Eagle medium 1/1 supplemented with 10% NU serum, choleratoxin, retinoic acid and antibiotics. We ovserved the morphologic changes with the phase-contrast microscope and the scanning electron microscope. In monolayer cultures, the epithelial cells grew to confluency on collagen gels, became squamous, and lost their cilia within 7 days. After floating the collagen gel, differentiation was noted. Seven days after floating, some cells were ciliated. Fourteen day after floating, nearly all cells were ciliated and some cells with microvilli were also observed. Our results show that the differentiation of human nasal epithelial cells into ciliated cells can be induced by floating the confluent epithelial cells with a collagen gel and this culture system will provide a good moddel for the study the function of human nasal epithelium in vitro.