OUTLINE: This a randomized, double blind, placebo controlled, multicenter study. Patients receive oral placebo daily for the first 4 weeks. Patients who comply with taking 80-100% of placebo are randomized to one of two treatment arms. Arm I: Patients receive oral eflornithine (DFMO) daily. Arm II: Patients receive an oral placebo daily. Treatment continues for 3-5 years in the absence of unacceptable toxicity. Patients who develop skin cancer during study undergo surgical excision and continue treatment on the arm to which they were originally randomized. Patients are followed every 6 months through year 5.