Breast cancer was induced in female Holtzman rats by intragastric administration of 7,12-dimethylbenz[a]antracene (DMBA). At tumor maturity, biopsies of viable tissue were obtained, frozen, and then assayed for estrogen, progesterone, and androgen receptor content. By simple linear regression analysis, progesterone receptor levels significantly correlated with both estrogen and androgen receptor levels, whereas estrogen and androgen receptor levels did not correlate with each other. Multiple regression analyses further substantiated the predictive value of the progesterone receptor for the other two hormone receptors. Knowledge of breast tumor androgen receptor levels may further enhance the value of the estrogen receptor and progesterone receptor in hormonal responsiveness. Further, the progesterone receptor may be the most sensitive of the steroid hormone receptors for selecting patients likely to respond to hormonal therapy.