Novel growth peptides derived from protein factors having molecular weights of about 22 and 45 kDa stimulate mitogenic activity of epithelial, but not fibroblastic cells, in particular, kidney epithelial cells. A source of the factors is scrape-wounded kidney epithelial cells in culture. Synthetic peptides having sixteen amino acids or less, in particular a hexapeptide, YPQGNH (SEQ ID NO: 2) maintain the mitogenic activity. The peptide AQPYPQGNHEASYG (14-Ser) (SEQ ID NO: 15) is effective in reversing acute renal failure in animals. The growth-promoting characteristics of the 22 and 45 kDa proteins and the peptides are useful in treating and diagnosing patients with kidney disease. Nucleotide sequences that encode the factor are useful to develop probes to locate similar factors, to identify genetic disorders involving the factor, and to produce the factor by genetic recombinant methods. The nucleotide sequences and fragments thereof, are also useful for diagnosis and treatment of kidney disorders.