There is very little information about human exposure to gaseous indoor air pollutants in the sleeping environment, even though the conditions in this environment are at least worrisome. The exposure during sleep is characterized by long exposure time, both absolute and relative, prevalence of specific pollutants and uncustomary proximity of sources to the breathing zone. This paper reports experimental results that show the impact of the proximity of possible emission sources such as a mattress, pillow and toy, on exposure of the sleeping subjects to these emissions. Based on full scale experiments in an environmental chamber using a breathing thermal manikin the intake fraction for gaseous pollutants are measured as well as the occurrence of rebreathing. Intake fractions for several sleep positions as well as different bedding arrangements are reported. The results show that human metabolism and corresponding heat release by the human body are dominant factors in the dilution of pollutants emitted in close proximity of the nose, reducing exposure by 40% compared to a case without metabolic heat output. This effect is more important than the sleep position. An important finding is that sleeping with the head under the covers increases intake by a factor 24 and results in a rebreathing rate of over 60%. (c) 2012 Elsevier Ltd. All rights reserved.