OBJECTIVE: The authors attempted to identify different patterns of improvement among patients receiving placebo during clinical trials. It was hypothesized that patients who improved abruptly would differ from patients whose improvement was gradual in that they would tend to improve earlier and would tend to have less persistent improvement. METHOD: The subjects were 144 patients who met the DSM-III criteria for depressive illness and were randomly assigned to placebo medication in four double-blind antidepressant drug trials. All studies lasted 6 weeks. Mood change was rated each week on a 7-point scale; a rating of 1 or 2 was considered an indication of improvement. Improvement was judged to be abrupt if the first score of 1 or 2 was immediately preceded by a score of 4 or worse, and it was classified as gradual if the first score of 1 or 2 was preceded by a score of 3 in at least 1 week. Improvement was considered persistent if a score of 1 or 2 was not followed by a score of 3 or worse in any subsequent week. RESULTS: Of the 144 patients, 72 showed clinical improvement during at least one weekly visit; 33 improved abruptly and 39 improved gradually. The abrupt improvements occurred significantly earlier in the trial and were less likely to persist than the gradual improvements regardless of when they occurred. CONCLUSIONS: These data suggest that among patients receiving placebo abrupt improvements are a form of placebo response and gradual responses may be the result of spontaneous remission. These preliminary observations require validation.Abstract Teaser