We evaluated the accuracy of a hand-held breath alcohol analyzer in the rapid determination of blood alcohol levels in the emergency patient with suspected ethanol intoxication. The Alco -Sensor III breath alcohol analyzer was used to measure alcohol levels in orally and nasally obtained end-expiratory breath samples in 55 patients. These levels were compared to directly measured blood alcohol levels. The patients were categorized into cooperative and uncooperative groups. The mean oral breath alcohol level obtained was 0.187 +/- 0.100 g/dL (range, 0.000 to 0.419) while the mean serum level was 0.217 +/- 0.113 g/dL (range, 0.00 to 400). The overall correlation between these two methods of measuring blood alcohol level was strong (r = .879, P less than .001). In cooperative patients the correlation was even stronger (r = .963, P less than .001), while in uncooperative patients the correlation was less but still significant (r = .723, P = .001). Nasally obtained samples correlated well with blood levels in cooperative patients (r = .874, P less than .001), but the correlation was less strong in uncooperative persons (r = .694, P = .003). Our study indicates that the Alco -Sensor III breath alcohol analyzer is sufficiently accurate to be of use in rapidly assessing blood alcohol levels, even when a patient is unable to cooperate fully.