In a retrospective study of 49 cases of carbon monoxide (CO) intoxication presented to the University of Illinois Hospital (UIH) Emergency Department between November 1986 and April 1988, we looked for a correlation between carboxyhemoglobin (COHb) as determined by a venous sample and the pH as determined by arterial blood gas analysis. The range of COHb levels in our study was 10-64% (mean 21.8% +/- 10.2%). Smoke inhalation cases (n = 3) were excluded from our study because they did not represent pure CO intoxication. Of the remaining 46 cases, 18 had arterial blood gases drawn. In none of these 18 cases (mean COHb 24.5% +/- 12.6%) did we find a correlation between COHb levels and the pH as determined by linear regression analysis. Also, in none of the 18 cases were there any therapeutic interventions associated with the arterial blood gas result. Additionally, in none of the remaining 28 cases were any therapeutic interventions performed with regards to patients' acidosis or ventilatory status (except 100% oxygen administration. We also retrospectively reviewed records of 104 cases who presented to Cook County Hospital Emergency Department with COHb levels over 10% during the period between March 1986 and May 1988. In these cases, we found no significant correlation between COHb level and arterial pH. We therefore conclude that arterial blood gases drawn in order to determine the degree of acidosis in mild CO intoxication without respiratory distress may not be useful in guiding therapeutic intervention and need not be routinely drawn.