Cyclosporin A (CSA) has been shown to prolong corneal allograft survival in a variety of animal models. Misoprostol is a prostaglandin E1 analogue with oral bioavailability and immunosuppressive properties. Misoprostol and CSA are synergistic immunosuppressants in vitro. In the present study, we evaluated the effect of adding misoprostol to a subtherapeutic dose of CSA in the orthotopic allogeneic rat penetrating keratoplasty model. Seventy inbred Lewis rats were recipients of orthotopic corneal allografts from Brown-Norway donors. Ten Lewis rats received orthotopic syngeneic grafts (Lew to Lew). Two separate experiments with 40 animals per trial were performed. In each trial, the rats were divided equally into four groups. Trial A: allogeneic control (A1), syngeneic control (A2), CSA at 10 mg/kg/d (A3), and CSA at 15 mg/kg/d (A4). Trial B: allogeneic control (B1), CSA alone at 7.5 mg/kg/d (B2), misoprostol alone at 1 mg/kg/d (B3), and CSA with misoprostol at 7.5 and 1 mg/kg/d, respectively (B4). Syngeneic control A2 as well as group A4 remained clear through postoperative day 22. The allogeneic control groups A1 and B1, plus treatment groups B2 and B3, rejected their grafts by postoperative day 12. Groups A3 and B4 demonstrated a delay in allograft rejection that continued to be statistically significant through the 12th postoperative day (p < 0.001). We conclude that the addition of systemic misoprostol to CSA can effectively prolong corneal allograft survival in the orthotopic allogeneic rat penetrating keratoplasty model.