To determine whether elderly (60-80 years old) depressed patients who cannot sustain a remission without medication must be maintained at full acute-treatment dose. To compare the efficacy of full-dose vs half-dose nortriptyline (NT) in preventing recurrences of major depression in the elderly. To determine whether those patients who experience a recurrence while in a maintenance placebo condition (Study I) require 100 percent of their acute-treatment dose of NT to prevent subsequent recurrences or can be successfully maintained on 50 percent of their acute-treatment dose (Study II).