Biogeochemical and functional gene experiments examined the nitrogen (N) cycle in geothermally heated soil (65-92°C, pH 3.9) located near the confluence of Rabbit Creek and the Firehole River in Yellowstone National Park (YNP). Nitrogen transformations examined included N₂ fixation, ammonification, nitrification, and denitrification. Aerobic incubations at 65°C yielded a net ammonification potential estimate of 0.19 µmoles NH₄⁺ g-soil^-1 • h^-1. As measured at 50°C, 65°C, and 80°C, denitrification potential ranged from 0.17 to 0.54 nmol N₂O • g-soil¹ • h^-1. Neither N₂ fixation (acetylene reduction) nor net nitrification (NH₄⁺ oxidation) was observed at these incubation temperatures. Using total soil RNA, no RT-PCR products were obtained with primers designed for nifH, amoA, nirK, or nirS amplification. However, PCRs with the same primers and DNA extracted from the thermal soil yielded amplicons having significant homology to nifH and nirK genes. In summary, our research suggests that microorganisms present in this thermal soil are capable of some N transformations, but evidence for a complete N cycle was not obtained.