Acute carbon monoxide (CO) intoxication was determined to be the cause of death for both infants, who were 2 months and 4 months old when they died 39 days apart in the same bed in the same bedroom. When the second infant died, investigation into the ambient air quality within the apartment revealed high levels of CO that came from a poorly ventilated, defective hot water heater located across a hallway from the bedroom where the two infants died. Toxicological analysis for CO was not performed on the infant who died first. The autopsy concluded that the infant's death was unexplained. Following the air-quality analysis of the apartment upon the death of the second infant, postmortem blood samples of the two infants were analyzed to reveal similarly elevated CO saturation levels for the two infants (13 percent and 14 percent). Nicotine and cotinine were not detected in the blood sample of either infant. Cherry-red livor mortis was absent. These two cases emphasize the importance of including an ambient air analysis and postmortem CO analysis as a routine part of a comprehensive investigation of sudden, unexpected infant deaths. 29 references