To the Editor: Michael Bauer, M.D., Ph.D., et al. (1) added to the compelling evidence that the supplementation of antidepressant treatment with lithium can enhance response in many treatment-resistant subjects with depression (2). Among patients with major depression and no evidence of bipolar disorder or suicidality who responded poorly to antidepressants for 1 month, 41 of 75 (54.7%) recovered with open-label lithium treatment added for 8–10 weeks. Of 30 who were followed up, one withdrew consent, and 29 were randomly assigned to continue lithium therapy (N=14) or to switch to placebo (N=15); antidepressant treatment continued up to 4 months. After lithium discontinuation, seven of the 15 placebo patients (46.7%) again became ill: five of the seven (71.4%) were depressed, and two (28.6%) were manic; one (6.7%) of the 15 placebo patients committed suicide. Therefore, two of 30 previously depressed unipolar patients (6.7%) (two of 15 patients taking placebo, 13.3%) were rediagnosed as bipolar. These responses all emerged within 4 months (mean=4 weeks) after they stopped taking lithium.