Introduction While a great deal is known about the human physiological response to acute carbon monoxide poisoning@ considerable controversy exists regarding possible psychophysical and behavioral effects resulting from carbon monoxide J exposures that produce carboxyhemoglobin (COHb) levels less than 20%. Since a variety of carbon monoxide exposure conditions can produce equivalent resultant COHb levels@ the major emphasis of this study was placed on the effects of specific COHb levels@ rather than the effects of certain carbon monoxide exposures. Since automobile drivers may have a higher risk of carbon monoxide exposure from automobile exhaust than the general population@ this study was designed to investigate the possible effects of COHb on driving related performance@ The scope of the investigation included first the development of r^id@ accurate laboratory and field COHb measurements in men. Next@ relation of the various levels of COHb to physiological performance@ simple and complex psychomotor skills@ driving performance@ and assessment of judgment degradation were studied. The complex laboratory tasks related to driving included: pursuit tracking@ choice reaction time@ and dual tasks (involving both pursuit tracking and choice reaction time tests performed simultaneously). The driving performance studies investigated 1) vehicle dynamics such as velocity and spacing while car following@ 2) operator control movements@ such as steering wheel@ gas@ and brake pedal applications@ and 3) perceptual measures@ such as driver's visual search and scan patterns measured with The Ohio State University eye-movement camera technique.