The mannanase (endo-β-1,4-mannanase; E.C. 126.96.36.199) and xylanase (endo-β-1,4-xylanase; E.C. 188.8.131.52) activity of five microfungal isolates from Antarctica were characterized at different temperatures and pH. In general, the hemicellulase activity of the antarctic strains occurred at least 10 °C and as much as 30 °C lower than that of a mesophilic reference strain. At 0 °C, two strains, a Phoma and a Penicillium, produced in excess of 40% of their measured maximum activity of mannanase. All strains had maximum hemicellulase activity in the range pH 4- 5, with Penicillium, Phoma and Alternaria strains exhibiting high (in excess of 80% of maximum) mannanase activity at pH 10. Three of the antarctic isolates exhibited high levels of xylanase activity over a pH range of 3-11.