Seven patients who had been maintained on tricyclic antidepressants developed signs of hypomania or mania shortly (two-seven days) after drug withdrawal. Three patients responded promptly to treatment with neuroleptics. One patient receiving lithium and three others who received no further drug treatment experienced more gradual resolution of symptoms. Tricyclic withdrawal is accompanied by changes in the turnover rate of individual neurotransmitters as well as by shifts in the equilibrium between various transmitter systems. These events may be accompanied by alterations in mood. Although relapse to depression is more common, hypomania or mania may also occur.