An efficient process has been developed for extraction of growth factors, antimicrobial agents, and minor whey proteins from bovine cheese whey. The whey-derived extract stimulates growth of mesodermal cell lines in culture but inhibits proliferation of epithelial-derived cells. Known growth factors characterised in the material do not account for its complete biological activity in cultured fibroblasts, suggesting the presence of unidentified cell mitogens. The protein extract is being investigated for use in prevention and repair of gastrointestinal injury and surface wounds. In preclinical studies with experimental animal models, the protein extract has been shown to reduce damage in the small bowel and oral mucosa associated with ablative cytotoxic drug regimens, as well as to promote healing of incisional and excisional surface wounds. Human trials of the whey extract incorporating novel protein delivery systems are now under way to assess its safety and efficacy. If successful, the whey-based extract will offer a valuable source of natural cell mitogens with widespread clinical application in preventing tissue damage and stimulating wound repair. Drug Dev. Res. 46:286-291, 1999.