Objective To determine whether a combined therapy with isosorbide mononitrate (40mg) and misoprostol (400mg) for pre-operative cervical ripening in the ®rst trimester would result in improved clinical effectiveness, and fewer side effects compared with each agent used alone.Design Randomised controlled trial. Setting Glasgow Royal In®rmary.Population Sixty-six primigravid women scheduled for suction termination of pregnancy.Methods Women were randomly assigned to receive before surgery, per vaginam, isosorbide mononitrate 40 mg (n 22), misoprostol 400 mg (n 22) or both agents together [isosorbide mononitrate 40 mg and misoprostol 400 mg] (n 22).Main outcome measures 1. To assess the cumulative force required to dilate the cervix to 8 mm; 2. the onset of new symptoms before termination of pregnancy. Conclusions We have not shown any advantage of combining misoprostol with the nitric oxide donor isosorbide mononitrate compared with misoprostol alone for pre-operative cervical ripening in the ®rst trimester.