In a building with geothermal utilization pit, concentrations of airborne microorganisms (cells/m3) by a filter sampler and temperature-humidity conditions were measured for one year to investigate seasonal change. The concentrations of indoor airborne microorganisms were affected by the pit air rather than outdoor air, especially in October. Temperature-humidity conditions between cooling season and heating season were relatively different both in the building and the pit. In October, one special species of fungi was observed on culture plates of the pit, and that implies that temperature-humidity conditions would affect the growth of the fungus.
