Stress is one of the more common reasons cited by addicts for continual drug use and relapse. Treatment approaches that target both drug-induced and stress-induced relapse may prove to be more beneficial than targeting drug-induced relapse alone. Lofexidine is a drug that reduces the physical symptoms of opiate withdrawal and may prove to have stress-reducing capabilites in drug addicts. The purpose of this study is to determine the maximal safe dose of lofexidine tolerated in naltrexone-treated heroin addicts and to find an optimal lofexidine induction schedule.