Objective: To determine the effects of misoprostol on plasma lipoprotein (a) concentrations of ovariectomized rats.Design: Controlled prospective study.Setting: Animal research laboratory.Animal(s): Four-month-old female Sprague-Dawley rats.Intervention(s): Blood samples were obtained before and 60 days after ovariectomy, and the rats were divided into three groups. Group I (five rats) was treated with vehicle (water); groups II and III (nine and eight rats, respectively) were treated with oral misoprostol at 100 and 200 μg/kg/d, respectively, for 60 days, after which blood was drawn again.Main Outcome Measure(s): Serum lipoprotein (a) levels.Result(s): The median lipoprotein (a) level before ovariectomy was 10.8 mg/dL (range, 10.6-46.5 mg/dL). Sixty days after ovariectomy, the level increased significantly to 15.9 mg/dL (range, 10.6-36.9 mg/dL). After treatment, there was no change in lipoprotein (a) levels in the vehicle-treated group (range, 16.3-21.1 mg/dL); however, the lipoprotein (a) levels decreased significantly in the group treated with 100 μg/kg/d of misoprostol, from 15.4 mg/dL to 10.8 mg/dL, and in the group treated with 200 μg/kg/d of misoprostol, from 17.1 mg/dL to 10.6 mg/dL.Conclusion(s): Misoprostol caused a significant decrease in lipoprotein (a) levels. 518 Copyright (C) 1999 American Society for Reproductive Medicine.