1. Nitrifying fungi were isolated from soil and were found to belong to the genera Aspergillus and Penicillium. 2. While the Aspergillus-isolates produced both nitrite and nitrate, the penicillia were observed to produce only nitrate from nitrite. Generally much larger amounts of nitrate were produced by the penicillia than by the aspergilli. 3. The results confirm and extend the observations of Schmidt, that soil fungi are capable of causing nitrification.