The efficacy and acceptability of two third generation oral contraceptives in Thai women were evaluated in a prospective, open, group-comparative, randomized, multicenter trial of women asking for contraception. In six Family Planning Centers and Outpatient Gynaecological Clinics in urban areas in Thailand, 783 healthy women who were at risk for pregnancy and did not have contraindications to oral contraceptive use were randomly allocated to one of the two study groups. An oral contraceptive containing 30 mcg ethinylestradiol and 150 mcg desogestrel was given to 394 women and an oral contraceptive with the same amount of ethinylestradiol and 75 mcg gestodene to 389 women during 6 cycles. Criteria of cycle control, side effects and the presence and severity of acne vulgaris were assessed and blood pressure and body weight measured at pretreatment and after cycles 1, 3 and 6. Furthermore, the efficacy was evaluated after the last cycle. No pregnancies occurred with either of the contraceptives. The incidences of irregular bleeding and minor side effects in both groups were very low and decreased after an initial increase in the first cycle. Acne improved in both groups. Blood pressure and body weight remained unchanged. The two oral contraceptives were found to be effective and acceptable in Thai women. Compared to Caucasian women, the incidences of irregular bleeding and side effects were apparently lower in these Asian women. Furthermore, the effects of both oral contraceptives were comparable.