A series of 16 epithelial cell lines derived from human carcinomatous and nonmalignant epithelial tissues were characterized for markers known to correlate with neoplasia in various model systems. The goal of these studies was to determine which in vitro transformation properties were relevant to human epithelial malignancy. The parameters tested were 1) colony formation in Methocel and on confluent monolayers of normal human epithelial cells and fibroblasts and 2) tumor induction in immunosuppressed mice. Cell lines derived from normal tissue and nonmalignant tissue peripheral to cancerous lesions were generally negative for these properties, whereas the carcinoma-derived lines varied in their expression (some lines being more abnormal than others). In most cases, the lines derived from metastatic lesions had more abnormal properties than did those derived from primary carcinomas.