Airborne fungi may contribute to the organic carbon (OC) content of particulate matter, which make them relevant to air pollution and climate change issues. This study aimed at assessing the contribution of fungal spores to the inhalable OC in indoor and outdoor environments in the Cincinnati metropolitan area. The contribution was calculated assuming that carbon content per fungal spore was 13 pg (derived from a report from Austria). Air samples were collected from 18 homes during summer. At each site, two air samples were simultaneously taken using Button Personal Inhalable Samplers for 24 hours. One sample was subjected to the total fungi enumeration and the other one was analyzed for OC with Thermal-Optical Transmittance technique. A (1-3)-β-d-glucan analysis was also conducted for indoor air samples using Limulus Amebocyte Lysate assay. Additionally, a questionnaire survey was performed on the various factors that might affect the indoor aerosol OC level. The total OC concentration ranged from 0.5 to 19.0 μg/m3 in outdoor air and from 0 to 36.2 μg/m3 in indoor air. The concentration of OC originating from fungal spores ranged from 3.8 to 958.4 ng/m3 in outdoor air while the respective range in indoor air was 0.8 to 351.2 ng/m3. The (1-3)-β-d-glucan was present indoors at levels ranging from 82.1 to 41,910 pg/m3. In contrast to studies performed in Austria, Australia and Britain, we found that fungal spores contribute rather little to the local outdoor OC. This could be due to different sampling instruments used for fungal spore sampling and regional differences in fungal spore concentrations. Even smaller contribution of fungal spores was found for indoor OC (average of 0.21%). Statistical analysis revealed that cigarette smoking was a significant factor for the indoor organic carbon level. The results indicate that smoking contributes to the indoor OC level more significantly than fungi.