Initially, the effect of water activity (aw) on heat resistance of Bacillus cereus spores (decimal reduction time) was investigated. A linear relationship was found between log D and 1-aw. The combined effects of temperature (85°C - 105°C), pH ( 4.5 - 6.5) and water activity (0.80 - 1) were then studied. A four parameter model was fitted to the data. This model appeared to be parsimonious with each parameter having a biological significance. Interactions between factors were observed but they accounted for  2.4% of the total variation and they were not taken into account by the model..