On January 9, 1996, CDC was notified about carbon monoxide (CO)-related morbidity and mortality associated with the blizzard in the northeastern United States. Most of these poisonings occurred among children and elderly persons and resulted from exposures in idling automobiles with exhaust pipes blocked by snow. This report summarizes three cases of CO poisoning reported to Philadelphia's Poison Control Center on January 8-9, and 22 cases reported in New York City on January 8-9.