Two novel epithelial cell growth factors (EpGF I and EpGF II) have beer purified to homogeneity from media conditioned by the embryonic lung fibroblast cell line, M426. The purified factors were subjected to NH 2-terminal sequence analysis and oligonucleotide probes were designed on the basis of the determined sequences. Hybridization of these probes to an M426 cDNA library identified positive clones for each factor. For each factor a representative set of clones was characterized by restriction mapping and DNA sequence analysis.