This six-cycle, multicenter, open-label, randomized study compared the clinical experience of two low-dose oral contraceptives (OC): a triphasic OC containing norgestimate (NGM) and 35 micrograms ethinyl estradiol (EE) (Ortho Tri-Cyclen) and a monophasic OC containing norethindrone acetate (NETA) and 20 micrograms EE (Loestrin Fe 1/20). Cycle control, lipid and androgen profiles, and user satisfaction were studied in new-start OC users (i.e., no prior use within 60 days). Breakthrough bleeding or breakthrough spotting (BTB/BTS) occurred in a significantly smaller percentage of NGM/EE users than NETA/EE users during each of six cycles (p < or = 0.002). The incidence of BTB/BTS ranged from 3.7% to 13.5% for NGM/EE users and from 23.5% to 49.7% for NETA/EE users. Significantly fewer NGM/EE users than NETA/EE users experienced absence of menses at cycles 2 through 6 (p < or = 0.003). The percentages of women having no menses at each cycle ranged from 0.9% to 4.7% for NGM/EE users and from 10.3% to 21.3% for NETA/EE users. NGM/EE users reported a significantly (p < 0.001) higher level of satisfaction with their OC at the end of six cycles than did NETA/EE users, but there was no significant difference in compliance, discontinuation rates, or adverse events between the two groups. NGM/EE produced a significantly (p < or = 0.001) greater beneficial effect on HDL-C, HDL2, and apo A-I than did NETA/EE. No statistically significant treatment differences were found for total cholesterol, LDL-C, triglycerides, or apo-B. Both OC increased sex hormone binding globulin and decreased free testosterone, but NGM/EE had a significantly greater effect (p < 0.009).