Four multicentre clinical trials on interruption of early pregnancy (less than or equal to 49 days of amenorrhea) using RU 486 have been conducted in China, including 2321 subjects. The data from trials 1, 2 and 4 are presented here. RU 486 (600 mg as a single dose) was given to 299 women. A further 422 women were given RU 486 (600 mg) plus a vaginal suppository containing the Chinese domestic prostaglandin PGO5 (1 mg) 36-60 hours later. Complete abortion was achieved in 63.5% of patients receiving RU 486 alone and in 94.1% of patients receiving RU 486 plus PG (p less than 0.001). RU 486 given alone showed decreasing efficacy as the duration of amenorrhea increased. However, RU 486 combined with PG was equally effective at all time points studied (less than or equal to 35 days of amenorrhea: 98.1%, 36-42 days: 92%, 42-49 days: 87.4%). When compared with RU 486 alone Ru 486 + PG also produced a shorter bleeding time and a lower volume of blood loss (n = 21, 52 ml vs n = 13, 117 ml). Two patients from the RU 486+PG group and 4 given RU 486 alone suffered heavy bleeding, necessitating emergency curettage. No transfusions were required. The time elapsed between RU 486 intake and expulsion of the conceptus was significantly shorter in the RU 486+PG group (n = 97, 31 days) than that in the RU 486 alone group (n = 95, 4.4 4.4 days). Main side effects, nausea/vomiting and headache/dizziness, were mainly due to RU 486. PG increased the incidence of diarrhea and uterine cramp.(ABSTRACT TRUNCATED AT 250 WORDS)