Milligram-range doses of E2 prostaglandins have long been used to induce labor or abortion in the second and third trimesters of pregnancy. Enprostil, a synthetic dehydroprostaglandin E2 structural analogue, is administered in microgram doses for the treatment of acute duodenal ulcer and acute gastric ulcer. This study examined the effect of the ulcer-healing dose and twice the ulcer-healing dose upon women in the first trimester of pregnancy. Two hundred and seven women who had requested legal abortion in the first trimester participated in two randomized, double-blind, placebo-controlled, parallel studies. They received two doses of enprostil 35 micrograms (the recommended dose for the treatment of duodenal and gastric ulcer) (n = 51), 70 micrograms (twice the recommended dose) (n = 53), or placebo (n = 103) 12 h apart. No drug-induced abortions occurred in any of the first-trimester pregnancies. Vaginal bleeding occurred in 4% of volunteers receiving the lower dose and 4% receiving the higher dose of enprostil. Vaginal bleeding occurred in up to 2% of volunteers on placebo. Although not recommended for pregnant women, if enprostil is given inadvertently to pregnant women with ulcers, it is unlikely to endanger the pregnancy during the first trimester.