In 21 healthy volunteers, a mapping of cortical areas from which motor evoked potentials in deltoid muscle and first dorsal interosseal muscle (FDI) could be elicited by focal transcranial magnetic stimulation was performed. For this purpose, magnetic stimuli were applied using a figure-of-eight shaped magnetic coil and a Magstim 200 stimulator at an intensity of 15% above motor threshold for the deltoid muscle. There was a considerable overlap between the cortical areas from which motor responses of the two muscles could be evoked with the FDI represented more laterally than the deltoid muscle. The cortical location from which maximal amplitudes of motor evoked potentials were elicited was 4-8 cm lateral of Cz with the FDI and 2-6 cm lateral of Cz with the deltoid muscle. Calculated centres of cortical points with maximal muscle responses were significantly separated with the FDI represented 5.7 cm lateral of Cz and deltoid muscle 4.3 cm lateral of Cz. The anterior-posterior extension of the cortical maps did not show significant differences between the proximal and distal arm muscle. In no subject an ipsilateral representation of either muscle could be found even when stimulating at maximal intensity.