This is a multicenter, randomized, double-blind placebo controlled Phase II pilot clinical trial. Objectives of the study are to: 1) Evaluate the ability of misoprostol to prevent oral mucositis in patients receiving preparative conditioning regimens for autologous stem cell transplant of either marrow or peripheral blood origin. 2) Evaluate the safety and tolerability of misoprostol 200 ug given orally every 8 hours compared to placebo in patients receiving preparative conditioning regimens for autologous stem cell transplant. This study is also being conducted at five other sites. The data for this multicenter study will be managed and analyzed with the assistance of the GCRC Systems Manager and the GCRC Biostatistician. Interim analyses are currently being performed to determine whether the misoprostol is safe and effective.