The effects of changing the stimulus presentation rate on early parietal (N20-P25) and frontal (P22-N30) somatosensory potentials (SEPs), evoked by median nerve stimulation, were investigated in 15 normal subjects. Stimuli were presented at 0.1, 0.4, 1.0, 4.0 and 10/sec. Only minor latency changes, mainly for the frontal P22 component, were observed when the stimulus rate was increased up to 10/sec: while the frontal P22-N30 complex was more rapidly and severely reduced in amplitude than the parietal N20-P25 complex. The differential effects of stimulus presentation rate on early frontal and parietal SEPs support the hypothesis of separate neural generators and suggest that the choice of the stimulation frequency may be critical for the interpretation of diagnostic SEP studies.