Data are presented at 25 sites using a British Standard test chart rather than a vision screening device. Assuming that the Department of Transport number plate test is equivalent to an acuity standard of between 6/12 and 6/9, it is estimated that between 1 percent and 3 percent of all drivers would fail the test at any given moment. Acuity was found to decline with age for drivers aged over 40 years. 5 percent and 10 percent respectively of drivers aged 65 over failed to meet the criteria of 6/12 and 6/9. A quater of all drivers tested were actually wearing spectacles or contact lenses prior to driving up to the testing station; only 15 of these drivers were wearing contact lenses. Qestionaire responses indicated that 64 percent of all drivers claimed to have had some form of eye test within the previous 3 years. The effects on drivers' acuity of type and use of optical prescription, and of length of time since last eye examination, are reported