['To investigate the changes in cortical excitability of the human motor cortex induced by high-frequency repetitive transcranial magnetic stimulation (rTMS) of different stimulation durations.', 'Twenty healthy subjects participated in the study. Subjects received 20 trains of 10-Hz rTMS at 80% of the resting motor threshold (RMT) intensity with two different stimulation durations (5 and 1.5s) over the motor hot spot for left first dorsal interosseous (FDI) muscle. Electromyographic responses (motor-evoked potentials, MEPs) to single-pulse stimulation, and intracortical inhibition (ICI) and intracortical facilitation (ICF) by paired-pulse stimulation were measured bilaterally in the relaxed FDI muscles before, immediately after, and 30, 60, 90 and 120 min after rTMS.', 'After 5s of 10-Hz rTMS, the mean amplitude of MEP for the stimulated M1 cortex decreased for up to 90min (P=0.002) and that of the unstimulated M1 cortex decreased for up to 60 min (P=0.008). Enhancement of ICI and suppression of ICF were observed and sustained for more than 90 min in both stimulated (P=0.001) and unstimulated (P=0.003) M1 cortex after 5s of 10-Hz rTMS. After 1.5s of 10-Hz rTMS, the mean amplitude of MEP increased in stimulated cortex for up to 120 min (P=0.005).'] Do changes in motor cortical excitability induced by high-frequency repetitive transcranial magnetic stimulation of different stimulation durations?