After conducting a randomized, 3-year maintenance trial in 128 patients with recurrent depression who had responded to combined short-term and continuation treatment with imipramine hydrochloride and interpersonal psychotherapy, we asked those individuals who survived the 3-year trial receiving active medication (with or without psychotherapy) to continue in a 2-year additional randomized trial of active medication vs placebo. The question was whether maintaining antidepressant medication at the dosage used to treat the acute episode beyond 3 years would continue to provide a significant prophylactic effect compared with medication discontinuation after the 3 years of effective maintenance treatment. Survival analysis demonstrated a highly significant continued prophylactic effect for active imipramine hydrochloride treatment maintained at an average dose of 200 mg. We conclude that active imipramine treatment is an effective means of preventing recurrence beyond 3 years and that patients with previous episodes less than 2 1/2 years apart, therefore, merit continued prophylaxis for at least 5 years.