['To examine changes in motor cortical excitability in adolescent subjects receiving 30 sessions of high-frequency prefrontal repetitive transcranial magnetic stimulation (rTMS).', 'Eight adolescents with treatment-resistant major depressive disorder (MDD) enrolled in an open augmentation trial of 10 Hz rTMS. Resting motor thresholds were obtained by the visualization of movement method with a maximum likelihood threshold hunting computer algorithm at baseline and after every five sessions of rTMS. Motor threshold was recorded as the percentage of total machine output at each measurement.', 'Motor threshold data from baseline, weeks 2, 4, and 5 were included in a mixed model repeated measure analysis to examine a change in least square mean effect over time. The omnibus effect did not reach statistical significance (F=1.25, p=0.32). However, multiple comparisons from the overall model demonstrated a decrease in the least square mean motor threshold. The mean contrast from baseline to week 5 approached significance (p=0.07). Moreover, a post-hoc analysis with a Wilcoxon signed ranks test demonstrated a significant decrease at week 5 (p=0.03).'] Do increased cortical excitability with prefrontal high-frequency repetitive transcranial magnetic stimulation in adolescents with treatment-resistant major depressive disorder?