The serial cultivation of human esophageal epithelial cells under clonal growth conditions has been achieved both under feeder and feeder-free conditions. Due to recent improvements in cultivation methods, the cells can be grown in the complete absence of serum. Experiments utilizing these cells in carcinogenesis studies are in progress. Cells exposed to Ni2SO4 gave rise to colonies with sustained growth properties. These cells are now being assessed for other properties indicative of cell transformation.