Environmental factors greatly affect the activity of soil microorganisms. However, not enough is known about how the environment affects the abundance and activity of many beneficial microorganisms after they are released into soil. Hirsutella minnesotensis is an important fungal parasite of nematodes and has shown great potential in nematode control. The objective of this study was to measure the effects of environmental factors on the abundance and activity of H. minnesotensis in soil. Fungal mycelium was mixed with dry soil (1% wet weight per dryweight) and placed into 50-mL plastic tubes. Soil temperature ranged from 5 to 30 degrees C; soil water content ranged from 6% to 22%; and the soil was supplemented with 0-70% of fine soil particles (silt and clay) or sand. After 24 days, fungal abundance was quantified by real-time PCR and its activity was inferred from the numbers of second-stage juveniles (J2) parasitized. The amount of H. minnesotensis DNA g(-1) soil and the percentage of J2 parasitized by H. minnesotensis were higher with lower soil temperature and water content, and higher fine particle content, demonstrating that H. minnesotensis has a greater potential to multiply and control pest nematodes in cooler, drier and heavier soils.