Significant differences in amylase, β-glucosidase, and phosphatase activities were observed among four Phytophthora cinnamomi isolates grown in nutrient-amended sterilized soil for 20 days. Amylase pH optima for the four isolates were within a relatively narrow range; at pH 5.5 each isolate was within 90% of its peak activity. Isolates SB-216-1, 1-281, and C-39 each exhibited maximal β-glucosidase activity at pH 5.0 and maximal phosphatase activity at pH 5.0–5.5. Maximal activity for these two enzymes of isolate A-7725 occurred at pH 3.5. In timed experiments, isolates 1-281 and A-7725 exhibited greater amylase activities than did the other two isolates. For β-glucosidase, greatest activity was observed for SB-216-1; activity of 1-281 was intermediate and least activity was observed for isolates A-7725 and C-39. Isolates SB-216-1 and 1-281 exhibited greatest phosphatase activities; isolate C-39 was intermediate in activity, and A-7725 was least active. Results indicate that significant differences exist among the isolates tested and that these differences can be quantitatively measured by the methods described.