Four-hundred-twenty-six women, aged 18 to 36, completed a four-cycle comparative, randomized, single-blind (observer blind), multicenter study of a new graduated estrogen formulation with three constant-dosed combination oral contraceptives containing the same synthetic steroid compounds. The products studied were Loestrin 1/20, Loestrin 1.5/30, Norlestrin 1/50, and a new graduated estrogen product, Estrostep. A total of 1,850 cycles were completed and analyzed for efficacy, side effects, metabolic changes, and cycle control. Four pregnancies occurred during the course of the study. None of the pregnancies occurred in the group receiving Estrostep. The new formulation produced the lowest rate of breakthrough bleeding (BTB) compared with the other three products. All four combination oral contraceptives resulted in an increase in high-density lipoprotein cholesterol (HDL-C). The levels of HDL-C were greatest with Estrostep.