Spraying the lower surface of the first true leaf (leaf 1) of cucumber plants with 50 mM K2HPO4 induced systemic resistance to anthracnose caused by Colletotrichum lagenarium, 2 to 7 days later. Within 16 h of application, the activities of peroxidase and chitinase increased in the induced leaf, and they continued to increase over the next 7 days reaching levels at least ten-fold higher than in leaf 1 of plants treated with water. During this period, the activities of both enzymes were usually two-fold or higher in leaf 2 of plants induced with K2HPO4 than in plants treated with water. If the induced plants were not further treated or mock-challenged with water on leaf 2, the enzyme levels increased slightly and levelled out at between two or four-fold higher than in the corresponding control plants. If plants were challenged with C. lagenarium on leaf 2, the enzyme activity at the site of challenge increased in the induced plants prior to rising in the control plants. Large increases in enzyme activity were only evident after the lesions became visible (3-4 days after challenge) in the control plants and this only occurred at the site of challenge. Seven days after challenge, the enzyme activities in the leaf tissue adjacent to the site of inoculation were similar in both the control and induced plants. Correlations were made between peroxidase and chitinase activities induced by several treatments on leaf 1 and the level of protection observed in leaf 2 after challenge with C. lagenarium.