The objective of this study was to integrate a systemic acquired resistance (SAR) inducing plant activator and available chemical control measures, consequently to determine if comparable efficacy with less chemical applications were possible. Variations in the activity of specific peroxidase enzymes that likely present the enhancement of host resistance were analyzed from the leaves of tomato seedlings after individual and combined applications. The efficacy tests of the compounds against several major diseases of tomato were conducted with replicated pot experiments under controlled conditions in the greenhouse. Possible correlations between higher efficacy of the compound in question and increased specific enzyme activity were evaluated with SPSS 8.0 for Windows. The highest efficacy for the control of both the late blight (Phytophthora infestans) and bacterial speck (Pseudomonas syringae pv. tomato) and the highest specific enzyme activities were obtained from Harpin(Ea)+ Experimental Aventis, and Harpin(Ea)+ Cupracol, respectively. Specific enzyme activities were increased about 148.5% and 126.0%, respectively. The results have revealed that comparable efficacies with combined applications of Messenger (Harpin(Ea)) as plant activator with fungicide or bactericide could possibly be efficacious and applicable in practice.