This study was performed to identify neuronal populations in the somatosensory areas engaged in discrimination of moving stimuli on the skin. Changes in regional cerebral blood flow (rCBF) were measured with positron emission tomography (PET) and correlated with cytoarchitectonic sensorimotor areas 4a, 4p, 3a, 3b, and 1. Volunteers discriminated differences in the speed of a rotating brush stimulating the palmar surface. Discrimination of moving stimuli, contrasted to rest, increased the rCBF mainly in primary somatosensory (S1) area 1, but also in area 3b. The parietal operculum (PO) was activated bilaterally. We conclude that area 1 is the area in S1 which is mainly responding to discrimination of moving stimuli and that the PO contains several regions engaged in the discrimination of fast transient stimuli.