In a static field study we tested drivers’ abilities to detect vehicles in the periphery of their direct fields of view while they gazed toward the driver-side exterior rearview mirror of a passenger car. The results indicate that both younger and older drivers can detect vehicles with reasonable efficiency even in far peripheral vision. However, the results also indicate that using peripheral vision entails a cost in terms of lengthened reaction time. Although that cost seems modest in comparison with the normal durations of glances to rearview mirrors and of direct looks to the rear, it is not clear from this study alone how the reaction time cost might influence the scanning strategies that drivers actually use in driving. The present study was oriented more to testing drivers’ basic visual capabilities than to outlining their overall strategies. Tentatively, it appears that the traditional way of defining the blind zone-by assuming a 180° direct field of view- is reasonably accurate. The forward limit of the blind zone would therefore be approximately 135° from the straight ahead when a driver looks toward a driver-side rearview mirror that is itself 45° from the straight ahead. Proposed solutions to the blind-zone problem, such as nonplanar mirrors with relatively wide fields of view, should therefore address the zone between the edge of a vehicle and a line about 45° out from that edge.