Aims: A better understanding of the role of antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT) in the protection of Aspergillus niger spores against thermal stress. Methods and Results: Conidiospores from A. niger 26 were subjected to wide range of temperatures (30, 50, 60 and 80 degrees C). The stress response was investigated by the determination of spore germination and mycelial growth of survivors under submerged cultivation. Exposure to any temperature above the optimal value induced an increase in SOD and CAT activities. PAGE demonstrated enhanced level of Cu/ZnSOD under stress conditions. We compared the influence of heat shock and superoxide-generating agent paraquat on growth and antioxidant enzyme defence and found different response to the both type of stresses. Conclusions: Heat stress elicits the enhanced synthesis of enzymes whose functions are to scavenge reactive oxygen species. These results suggested an association between thermal and oxidative stress. Significance and Impact of the Study: Evidence is provided for the possibility that oxidative stress plays a major role in the effect of heat in low eucaryotes such as A. niger. This knowledge may be of importance in controlling both fermentation and pathogenicity.