Visual and somatosensory evoked potentials were mapped in the cerebral cortex of adult rats and, after filling the cerebral arteries and veins with dye, the mappings were then compared to the distribution of pial veins. A close relationship was found between the position, size and shape of the occipital venous drainage field and the distribution of visual evoked potentials with high amplitudes and short latencies. Accordingly, such potentials evoked by stimulation of the forepaw and tailroot were confined to the fronto-parietal drainage field. In the case of individual variations in the expansion and shape of sensory areas, the medial and lateral borders of the occipital drainage field and the medial border of the fronto-parietal drainage field covaried. Only at the common border between these two drainage fields, visual evoked potentials with small amplitudes and long latencies extended into the parietal drainage field and overlapped with somatosensory evoked potentials. This overlapping area corresponds in position to the anterior part of the peristriate cortex. A comparison between the vascular organization and cytoarchitectonic maps of the rat cortex indicates that other parts of the characteristic pattern of venous drainage fields may also correlate with the cytoarchitectonic and functional organization of the cerebral cortex. These observations suggest that during morphogenesis the formation of sensory projections to the cerebral cortex may interact with the angiogenesis, mainly with the development of veins.