In December 2007 and January 2008, the Centers for Disease Control and Prevention (CDC) measured formaldehyde levels in a stratified random sample of 519 FEMA- supplied occupied travel trailers, park models, and mobile homes (i.e., "trailers"). At the time of the study, sampled trailers were in use as temporary shelter for Louisiana and Mississippi residents displaced by hurricanes Katrina and Rita. The study aimed to determine formaldehyde levels in occupied trailers, determine trailer characteristics that could affect formaldehyde levels, and provide information to assist FEMA in deciding whether to relocate residents from FEMA-supplied trailers in the Gulf Coast area. This study assessed only current formaldehyde levels in the occupied trailers; it was not a health effects study.