OBJECTIVE To find the effective dose of intravaginal misoprostol to induce second trimester abortion. METHODS Intravaginal misoprostol in 200-microg, 400-microg and 600-microg doses were applied at 12-h intervals in 150 consecutive pregnancies. RESULTS The 48-h successful abortion rate was 70.6%, 82% and 96%, respectively, and these rates were unaffected by parity. The mean induction to abortion interval was 45.0 +/- 41.5, 33.4 +/- 34.9 and 22.3 +/- 14.3 h, respectively. The mean dose of misoprostol required to induce abortion was 416.7 microg, 772.8 microg and 1296 microg. The rate of nausea and vomiting was 3.9%, 12% and 20%. The diarrhea occurrence rate was 0%, 6% and 22% with temperature elevation 0%, 2% and 28%, respectively. The rate of incomplete abortion was 35.3%, 28% and 22%, respectively. CONCLUSIONS The 600-microg dose is more effective as an abortifacient agent for second trimester abortion in terms of 48-h success rate and the rate of incomplete abortion but with more side effects. However, the side effects were mild and did not warrant any specific treatment.