132 microorganisms, isolates from soil and decayed fruits, were tested for phytase production. All isolates intensively producing active extracellular phytase were of fungal origin. The most active fungal isolates with phytase activity were identified as Aspergillus niger. At the end of the growth phase, the extracellular phytase activity produced by A. niger strain 92 was 132 nkat/mL, with strain 89 it was 53 nkat/mL. In both strains the extracellular enzyme activity exhibited two marked activity optima at pH 1.8 and 5.0 and a temperature optimum at 55 degrees C.