A controlled investigation was made of the rehabilitative efficacy of brief residential psychedelic (LSD) psychotherapy with chronic heroin abusers. Seventy-eight volunteer addict inmates from Maryland correctional institutions were randomly assigned to the following: a treatment condition–psychedlic therapy (incorporating one high-dose LSD administration) during a six weeks residence in a halfway house type of facility; or a control condition–an outpatient clinic program including daily urine monitoring and weekly group psychotherapy. All subjects (37 completers in each group) were treated identically save for the initial six-week period of residential treatment. Major outcome criteria were based on evaluative assessments (including daily urine surveillance) of the treatment and control groups covering the 12 months following discharge to the community. Comparative verified abstinence data throughout the first posttreatment year were significantly in favor of the treatment group.