To investigate the effect of individual formulations of oral contraceptives (OCs) on the risk of breast cancer in women, the authors analyzed case-control data from the Cancer and Steroid Hormone Study of the Centers for Disease Control. The cases were 4711 women ages 20-54 with breast cancer diagnosed between December 1, 1980-December 31, 1982 through 8 population-based tumor registries located throughout the US. The controls were 4676 women of the same ages selected by the random digit dialing of households with telephones in the same geographic regions covered by the registries. Women were interviewed in the home according to a pretested standardized questionnaire. A photobook of all OCs marketed in the US since 1960 and a calendar were used to assist in the recall of the use of OCs. Compared with women who had never used OCs, women who had used them had a relative risk of breast cancer of 1.0. Women who used OCs for up to 5 years, 6-9 years, 10-14 years, and longer than 14 years had relative risks of 1.0, 1.0, 1.1., and 0.6, respectively, when compared with women who had never used OCs. Among women who had used only 1 OC formulation, the relative risks of breast cancer ranged from 0.6-1.6. Women who used combination OCs containing only mestranol or only ethinyl estradiol as the estrogen component had relative risks of 1.0. Similarly, analyses according to the specific progestin component in combination OCs (ethynodiol diacetate, norethindrone, norethindrone acetate, norethynodrel, and norgestrel) did not suggest an increased risk of breast cancer. Women who had used combination OCs before their 1st fullterm pregnancy had a relative risk of breast cancer of 1.0, compared with parous women who had never used OCs. Finally, the relationship between the use of combination OCs and the risk of breast cancer did not appear to be modified by menopausal status or a family history of breast cancer. These findings provide further support for the contention that OC use does not increase the risk of breast cancer in women. (author's)