This is an initial descriptive report of two morphologically different cell lines (SKG-3a and SKG-3b) obtained from a human uterine cervical epidermoid carcinoma. These sublines were found to be derived from a moderately differentiated epidermoid carcinoma partially mixed with clear cell components. Both sublines had already been subcultivated more than 80 times since the initial separation. SKG-3a cells were much smaller in size and volume than 3b. The numbers of chromosomes were almost identical. Their cytology revealed anaplastic and pleomorphic features. SKG-3a was positive with periodic acid-Schiff stain and this changed to negative after an amylase digestive test, suggesting that the cells contained glycogen. An electron-microscopic examination confirmed the presence of many glycogen particles in 3a cytoplasm, but few in 3b. Tonofilaments and desmosomes were observed in both cytoplasms, suggesting epidermoid origin. In nude mice, SKG-3a produced clear cell epidermoid carcinoma with much glycogen, while 3b grew as a moderately differentiated epidermoid carcinoma with little glycogen. It is concluded that SKG-3a is derived from the clear cell epidermoid carcinoma and 3b is from the moderately differentiated epidermoid carcinoma. It is also clear that both were more heat sensitive at and over 39 degrees C than normal cells.