Growth of the human endometrial carcinoma Ishikawa cell line was stimulated by transforming growth factor-beta-1 when cultured in serum-containing and chemically defined culture medium. This response was not unique to endometrial carcinoma cells, as the breast-cancer cell line, T47-D, was similarly stimulated by TGF-beta-1, TGF-beta-1, stimulated growth of MCF-7 breast-cancer cells in chemically defined medium but inhibited growth of this cell line in serum-containing medium. The data provide a demonstration of a positive growth response to TGF-beta-1 in oestrogen-receptor-positive cells and do not support the hypothesis that this growth factor is simply a negative growth regulator in epithelial-cancer cell lines.