Two triphasic oral contraceptives containing gestodene (GES) (a new progestogen) and levonorgestrel (LNG) were compared with respect to contraceptive effect, cycle control, acceptability and side effects. The serum concentrations of ingested hormones were measured together with ovarian, pituitary, and some adrenal hormones, as well as sex hormone binding globulin (SHBG). The contraceptive effect and cycle control were good with both preparations, and there were only a few minor side effects. SHBG was elevated 2-fold in the LNG group and 3-fold in the GES group. The GES concentration in serum varied more than the LNG concentration, but with correction for variations in SHBG binding, less variability in actual GES and LNG concentrations was seen. Serum levels of FSH, LH, estradiol and progesterone were all depressed with both preparations. The depression was more marked in the GES group, despite lower progestogen ingestion and similar serum concentrations. Equal decreases were found in testosterone, androstenedione and dehydroepiandrosterone sulfate (DHEA-S) with both preparations.