Modafinil is a wake-promoting agent approved by the Federal Drug Administration for the treatment of narcolepsy. Preliminary evidence indicates that modafinil may improve fatigue and excessive sleepiness associated with a variety of conditions. The purpose of this study was to investigate the utility of modafinil as an adjunctive treatment of depressed patients. Subjects with a history of major depression with partial response on a stable therapeutic dose of an antidepressant were eligible to participate. All subjects endorsed complaints of significant fatigue and/or excessive sleepiness on clinical assessment. Modafinil was added to their existing regimen at a dose of 100 to 400 mg/d for 4 weeks. Subjects were assessed at 2-week intervals for improvement using the standard depression scales (HDRS, BDI, CGI), fatigue scales (VASF, FSI), and a neuropsychologic battery. Thirty-five subjects were entered and 31 subjects completed the 4-week trial. Significant improvements were seen across all 3 measures of depression (HDRS, BDI, CGIS) and both measures of fatigue (VASF, FSI). On the neurocognitive battery, significant gains in the Stroop Interference Test were seen at 4 weeks, whereas the other cognitive tests showed no change. Modafinil may be a useful and a well-tolerated adjunctive agent to standard antidepressants in the treatment of major depression.