Norethisterone oenanthate was given as an injectable contraceptive to 126 Thai women. Only healthy informed volunteers aged 18–35 years were admitted to the study. One ml of oily solution containing 200 mg of steroid was administered into the gluteal muscles. The first injection was given during days 1–5 of a normal menstrual period. The second, third and fourth injections were given at eight-week intervals and were followed by subsequent injections at 12-week intervals. All injections were given within seven days of the scheduled date. Volunteers were instructed to record any vaginal bleeding in diary cards. At each visit, weight, blood pressure and menstrual bleeding were recorded. Complaints and adverse effects were also noted. Prior to admission for study, an oral glucose tolerance test (OGTT), serum transaminase, cholesterol and triglycerides were simultaneously studied in 21 women and then repeated at three, six and twelve months. The 12-month continuation rate was 63 100 women-years with 5 accidental pregnancies. Two pregnancies occurred during the second injection intervals and the other three pregnancies occurred during the third, fourth and fifth injection intervals. The 12-month study revealed 11 100 and 25 100 women-years of amenorrhea and heavy bleeding, respectively. There was a statistically significant increase in the serum glucose tolerance test (P < 0.05) at the 30-minute time intervals after 12 months of use, but the areas under the curves were within normal limits. The total cholesterol and triglycerides showed a significant transient decrease (P < 0.01) at the third month of study and returned to normal after 6 months.