Some studies suggest that more severely ill patients with depression respond well to antidepressants and poorly to placebo, whereas those who are mildly ill respond equally well to antidepressants and placebo. This notion has implications for the design of clinical trials. To further assess and substantiate these putative predictors of antidepressant and placebo response, we assessed the Food and Drug Administration database of 45 phase II and III antidepressant clinical trials. The frequency of statistically significant differences between antidepressants and placebo was higher in the trials that included patients with more severe depression. In the antidepressant-treated groups, the magnitude of symptom reduction was signif-icantly related to mean initial Hamilton Rating Scale for Depression (HAM-D) score; the higher the mean initial HAM-D score, the larger the change. With placebo treatment, however, the higher the mean initial HAM-D score, the smaller the change. Early discontinuation was more frequent among patients whose mean initial HAM-D scores were higher. These data may help inform the design of future antidepressant clinical trials.