Venous BAC was measured by headspace gas chromatography, and BRAC was determined with an infrared analyzer. Blood samples were always taken after breath tests were made, and the average time delay was about 30 minutes. Blood/breath ratios of alcohol decreased as the time between sampling blood and breath increased. The overall mean time-adjusted blood/breath ratio was 2,407 and 95 percent limits of agreement were 1,981 and 2,833. During 1992, 1993, and 1994, mean blood/breath ratios of alcohol were remarkably constant, being 2,409, 2,407, and 2,421, respectively, and values were not significantly influenced by age, gender, or blood alcohol content. In 34 individuals (4.3 percent), the blood/breath ratio was less than 2,100 after compensating for the metabolism of alcohol between the times of sampling blood and breath. This compared with 156 individuals (19.6 percent) who had a blood/breath ratio of less than 2,100 without making any correction for the metabolism of alcohol. 20 references, 5 tables, and 5 figures