9-Deoxo-16, 16-dimethyl-9-methylene-PGE2 is a new prostaglandin analogue which is stable in suppository form. Estimates of potential for gastrointestinal side effects in monkey in vivo indicated that the frequency of diarrhea was low with retention of uterine stimulating potency. In the present study the effect of the compound on uterine contractility and its efficacy for cervical dilatation and for termination of pregnancy during the second trimester was evaluated in 89 women. The uterine stimulating potency of 9-deoxo-16, 16-dimethyl-9-methylene-PGE2 during mid-pregnancy following bolus intravenous injection or intravenous infusion was four to five times that of PGE2 alpha. Pretreatment with one single vaginal suppository containing 40 mg of the 9-methylene analogue resulted in dilatation of the cervical canal sufficiently to allow evacuation of the uterus without further dilatation in most patients in the 13th to 14th week of pregnancy. In more advanced pregnancies (15th to 24th week of gestation), 83 percent of the patients aborted following vaginal administration of 75 mg of the compound at 0 and 8 hours. All patients had aborted 42 hours after start of treatment if intramuscular injections of 15-methyl-PGE2alpha Tham were added after 24 hours. Both treatments were associated with a significantly lower frequency of gastrointestinal side effects than following vaginal administration of 15-methyl-PGF2alpha methyl ester. The incidence of temperature elevation on the other hand seemed to be higher.