Excitatory discharges evoked by stimulating the central part of classical receptive fields may be facilitated or inhibited by flanking targets. The sign of modulation depends on contrast in the excitatory center: a weak contrast facilitates the response, a strong contrast inhibits. We investigated these influences in a pool of units whose activity was simultaneously recorded. In cats multiunit recordings were performed in area 17. Cells were stimulated with a 50% contrast, central sine-wave patch and a peripheral patch (same orientation, luminance, spatial and temporal frequencies as the central patch) was applied. The contrast of the peripheral target was modulated from 0 to 100%. Single cells were sorted out from the multiunit pool and the response magnitudes of individual cells were analyzed in relationship to the differential contrast. Sorting out individual spikes from the original pool revealed that two neighbouring units react in different and sometimes opposite fashion to the same differential contrasts. In addition, complex cells seem to be sensitive to the contrast of the peripheral targets specific differences in contrast facilitate discharges, whereas simple cells fail to show such sensitivity. Results suggest a coding process for contrast.