A newly isolated thermophilic fungus was found to produce a partially inducible extracellular DNase. This manuscript focuses on the characterization of this novel thermophilic DNase in terms of optimal enzyme conditions, molecular weight, and certain kinetic properties. The DNase was found to be inactivated by the presence of EDTA demonstrating its dependence on metal cofactors for activity. Maximum activity occurred at pH 6.0 with no activity at pH 2.0 or 10.0. The optimal temperature for the purified DNase was 65 A degrees C. The thermophilic DNase was found to be an exonuclease with an estimated molecular weight of 56 kDa.