Blood alcohol concentrations (BAC) and corresponding breath alcohol concentrations (BrAC) were determined for 21,582 drivers apprehended by New Zealand police. BAC was measured using headspace gas chromatography, and BrAC was determined with Intoxilyzer 5000 or Seres Ethylometre infrared analysers. The delay (DEL) between breath testing and blood sampling ranged from 0.03 to 5.4 h. BAC/BrAC ratios were calculated before and after BAC values were corrected for DEL using 19 mg/dL/h as an estimate of the blood alcohol clearance rate. Calculations were performed for single and duplicate breath samples obtained using the Intoxilyzer (groups I-1 and I-2) and Seres devices (groups S-1 and S-2). Before correction for DEL, BAC/BrAC ratios for groups I-1, I-2, S-1, and S-2 were (mean+/-SD) 2320+/-260, 2180+/-242, 2330+/-276, and 2250+/-259, respectively. After BAC values were adjusted for DEL, BAC/BrAC ratios for these groups were (mean+/-SD) 2510+/-256, 2370+/-240, 2520+/-280, and 2440+/-260, respectively. Our results indicate that in New Zealand the mean BAC/BrAC ratio is 19-26% higher than the ratio of the respective legal limits (2000).