MT2 cells, a clonal cell line of MTW9/PL cells originally obtained from a mammary adenocarcinoma, from estrogen-responsive tumors in Wistar-Furth rats. o,p'-DDT supports MT2 tumor growth at a rate similar to 17 beta-estradiol. This effect of o,p'-DDT is dose-dependent and specific, since the DDT congener p,p'-DDD, which does not bind to tumor estrogen receptors, does not support tumor growth. This is the first demonstration that DDT can support the growth of an estrogen-responsive tumor.