We examined the efficacy and tolerability of augmentation with an extended release formulation of methylphenidate (OROS MPH, Concerta) in patients with major depression who were nonresponders or partial responders to antidepressants. Sixty subjects with treatment-resistant depression (TRD) participated in a 4-week, randomized, double-blind, placebo-controlled study of augmentation with methylphenidate (18-54 mg/d). The preexisting antidepressant dose was unchanged. The primary efficacy measure was change in the 21-item Hamilton Depression Rating Scale from randomization to end of treatment. Data were analyzed with intent-to-treat with last observation carried forward approach. There were no statistically significant differences between the methylphenidate (n = 30) and placebo (n = 30) groups in reduction in 21-item Hamilton Depression Rating Scale scores (drug, -6.9; placebo, -4.7) from baseline to end of treatment (F1,47 = 1.24, P = 0.22), although responders were numerically higher in the extended-release methylphenidate group (40.0%) than in the placebo group (23.3%). On the secondary efficacy measures of changes in Clinical Global Impression-Improvement and Severity scores and Beck Depression Inventory-Second Edition, the drug failed to separate from placebo, although the proportion of responders in the drug group were numerically higher than placebo. There were no significant differences in weight, heart rate, and blood pressure changes between the 2 groups. The common adverse events were loss of appetite, nausea, headache, and anxiety. The mean dose of drug was 34.2 mg/d. The study did not demonstrate a statistically significant benefit for augmentation with methylphenidate in TRD. Combination of methylphenidate with antidepressants was well tolerated. Adequately powered, randomized, controlled trials are necessary to fully evaluate the efficacy of extended-release methylphenidate in TRD.