The effect of a low dose triphasic oral contraceptive (OC) was evaluated during a 6-month treatment period in 41 patients (mean age, 25.4 +/- 0.7 yr) who had grade I-IV postpubertal acne and normal menses. The OC contained three dose levels of ethynyl estradiol and dl-norgestrel. Acne lesions were assessed, and serum androgen levels were measured during a control cycle and between days 17-21 of treatment cycles 1, 2, 3, and 6. Four patients dropped out after 3 months of treatment. Acne was significantly improved after the first OC cycle. After six cycles, the number of comedones had decreased by 79.6 +/- 3.2% (range, 50-100%) in 69.4% of the patients. Mean baseline levels of testosterone, 17-hydroxyprogesterone, and dehydroepiandrosterone sulfate were in the upper third of the normal range, with elevated individual values in 18.9%, 36.5%, and 26.8% of the women, respectively. Mean baseline levels of androstenedione, free testosterone (T), and 3 alpha-androstanediol glucuronide (3 alpha-diol-G) were above the normal range, with elevated individual values in 51.2%, 75.0%, and 85.4% of the patients, respectively. Sex hormone-binding globulin (SHBG) levels were below the normal range in 26.8% of the cases. At the end of the first OC cycle, there was a significant (P less than 0.01) decrease in all androgen precursors and a 2-fold increase in SHBG. Androstenedione and free T decreased into the normal range during OC intake. Serum 3 alpha-diol-G levels remained elevated, but had decreased by 34.5% at cycle 6 (P less than 0.05). These results show that the triphasic OC has significantly improved acne in postpubertal women for whom acne was the main manifestation of mild hyperandrogenic activity. The improvement in acne corresponded to a decrease in adrenal/ovarian androgens and free T, which led to a decreased metabolism to 3 alpha-diol-G, presumably by the sebaceous glands. The increase in SHBG is considered an estrogenic effect, and the triphasic formulation containing low dose dl-norgestrel is not androgenic but, rather, an estrogen-dominant formulation; as such, this product is recommended in women requiring contraception who also have idiopathic acne.