Tried to determine the cognitive effects of daily repetitive transcranial magnetic stimulation (rTMS) administered under the conditions of a treatment trial for major depression. In a randomized double-blind treatment study, 10 Ss with an episode of major depression received either 2 wks of low-frequency (1 Hz) or high-frequency (20 Hz) rTMS (800 pulses, 20 trains over 20 min, 80% of motor threshold, 5 days per wk) to the left dorsolateral prefrontal cortex and then were crossed over to the other treatment condition. Ss received cognitive testing at baseline and after the 1st and 2nd wks of low- or high frequency rTMS, which was examined by repeated-measures ANOVOut of 16 cognitive measures tested after 1 or 2 wks of rTMS compared with baseline status, none showed deterioration, and the only significant main treatment effect indicated improvement on a list-recall test from pre- to post rTMS after 1 wk. These preliminary data suggest no gross deleterious cognitive effects of 2 wks of 1- or 20 Hz rTMS at 80% of motor threshold over the left prefrontal cortex. Further cognitive studies of the effects of rTMS at other parameters used in clinical trials for mood disorders remain to be undertaken.