Patient blindability was examined in clinical, psychopharmacological, double-blind, placebo-controlled trials involving medications for obsessive-compulsive disorder and major depression. Based on the presence of clinical improvement and side effects, patients were able to determine correctly whether they took medication versus placebo. On the basis of these preliminary findings, the authors question the blindability of patients in clinical trials. Implications for the continued use of double-blind, placebo-controlled trials are discussed.