A hyper-producing strain of Aspergillus niger var teigham was used for the production of phytase in shake flask and fermenter. This newly isolated strain maximally produced 184 nkat/ml phytase activity in minimal medium with a specific activity of 21367 nkat/mg protein. The optimum growth temperature of A. niger was 37 degreesC while maximum enzyme activity was obtained when the organism was grown at 30 degreesC and at an initial pH of 6.5. Among the various carbon sources used, a combination of glucose and starch (3 and 1%, respectively) was found to be optimum for phytase production. Although biopeptone and ammonium nitrate gave the maximum enzyme yield, the specific activity of phytase was comparatively higher when ammonium nitrate was used as sole source of nitrogen. A sharp decline in phytase production was observed even at 0.05% phosphorous in the medium with no production at 0.1% and above, indicating end product inhibition in phytase synthesis. In shake flasks, the productivity of phytase was 10824 nkat/l.d while fermenter productivity was 20 000 nkat/l.d. (C) 2002 Elsevier Science Ltd. All rights reserved.