Poisoning due to "non-automobile" gas-powered engines accounts for the largest proportion of occupational carbon monoxide (CO) poisonings in Colorado workers. The present analysis was undertaken to characterize the problem and develop prevention strategies. Cases of occupational CO poisoning were identified from Colorado's population-based surveillance system for unintentional CO poisonings. For cases poisoned by "non-automobile" gas-powered engines, medical records were obtained. Results showed that almost all of the poisonings from these engines occurred indoors or in an enclosed space. Concrete saws were the most frequent source of poisoning. When compared with operators of other equipment, concrete saw operators had shorter durations of exposure to CO but generally experienced more severe symptoms and signs of poisoning. These results underscore the hazard associated with the indoor use of any gas-powered equipment; however, operators of concrete saws may receive a higher dose of CO.