A method is presented for 160hydroxylase (SAH) induction in cultured human lymphocytes. SAH, a microsomal-associated enzyme, effects the oxidative conversion of 17pestradiol to estriol, which competes for cytoplasmic binding sites. 17,-estradiol and estrone are known mammary carcinogens, while estriol and its epimers have been suggested to have anticarcinogenic properties. To substantiate genetic variations of hydroxylase activity, an analysis of estrogen-induced cultured human lymphocytes was conducted to evaluate the frequency distribution of low, intermediate, and high SAH activity. Frequency analysis indicated that the control population distribution of SAH activity does not corroborate a proposed trimodal expansion of human SAH activity. A log normal distribution of SAH activity does exist, which suggests a polygenic mode of genetic control. SAH activity in a population of breast cancer patients and relatives of breast cancer patients showed no statistical difference from the SAH activity in the control population.