This study characterized the levels of bioaerosol contamination of indoor air environments. Significant findings of the study include: 1) Fungi and respirable bacteria concentrations were significantly higher in basements, while CO2 levels were higher on the main floor; 2) Healthy homes had indoor viable fungal concentrations 30 to 50% of the outdoor levels, whereas sick homes had levels over 60%. Strong seasonal effect was seen from measurements of outside fungi but this was not reflected in indoor concentrations; 3) CO2 concentration was not associated with bioaerosol concentration; basement relative humidity was associated with increased airborne fungi; central air conditioning and increased air conditioner use were associated with lower microbial concentrations; lower Penicillium and Aspergillus airborne spores were associated with high efficiency furnace filters; and homes with finished basements had significantly lower microbial concentrations; 4) Tests of association using survey results showed age of occupant and the presence of smokers in the house to be significantly associated with increased self-reported health symptoms, including watery eyes, drowsiness, backaches, muscle/joint pain, indigestion, nausea, and flaky skin; and 5) Methodologies using the Anderson microbial sampler and the Burkard spore sampler demonstrated excellent agreement between theses two methods of air sampling.