The development of tissue culture systems for propagation of human epithelial cells has aided the investigation of events that lead normal epithelial cells to become neoplastic. The establishment of human epidermal keratinocyte and human bronchial epithelial cell lines and their usefulness for oncogenic virus assay systems are described. In addition, cultivation of primary epithelial culture from oral hairy leukoplakia and normal salivary gland biopsies in a serum-free medium is discussed.