A police "booze" bus was used to obtain a systematic sample of breath tests from drivers in Perth, Western Australia between 2200 and 0300 on Thursday, Friday and Saturday nights over about six weeks in September and October, 1999. Of the 8616 tests, 1.92 per cent were over 0.05gm per cent, the legal limit. There was a higher percentage of drivers with an illegal blood alcohol concentration (BAC) on Friday nights and after midnight compared with other times. The blood alcohol distribution of survey drivers was compared with that of drivers involved in crashes during the same hours and days of the week for 1997. The ratio of crash to survey drivers at a BAC of 0.05 was about 5:1, at 0.08, about 25:1 and over 0.150, about 80:1. This survey has provided a baseline description of the drink driving behaviour of drivers in Perth for comparison with subsequent surveys in following years.