Color differences required for fast parallel searches were measured for small and large display fields. The main purpose of the measurement was to test the hypothesis that serial searches obtained with small color differences in large display fields are due to poor discrimination in the peripheral visual field and to the need for foveal fixation. Results do not support this hypothesis but show that the color differences required for parallel search are just as large in a display confined to an area roughly the size of the fovea as in a large display. However, results also show that the color difference required for a fast, parallel search is dependent on the size of the stimuli in a large display field. This result is consistent with the possibility that poor discrimination in the periphery may contribute to the size of the required differences if the stimuli are small.