Systematic building studies which have focused on a population of buildings or intensive studies of one or more problem buildings have attempted to determine whether significant relationships exist between symptom prevalence rates and a limited number of relatively easily measured or assessed gas/vapor-or particulate-phase contaminants. These have included the bioeffluent carbon dioxide (CO2), combustion by-products such as carbon monoxide (CO), formaldehyde, volatile organic compounds (VOCs), and particulate matter. Though bioeffluents are widely believed to contribute to comfort problems in buildings, there is little direct evidence to implicate bioeffluents as determined from CO, levels in buildings. In addition to formaldehyde, a large variety of organic compounds have been reported to be present in office and other nonresidential nonindustrial buildings. Organic compounds, particularly VOCs, have been suspected to be causal or risk factors for sick building syndrome (SBS) symptoms. With a few exceptions, formaldehyde levels in office and public-access buildings have been considered to be too low to cause reported SBS symptoms.