Expression of proteinase inhibitor I and II genes was investigated during infection by Pseudomonas syringae pv. tomato, the causal agent of bacterial speck disease in tomato. Inoculation of leaves with P. s. pv. tomato of two inbred tomato lines that are resistant and susceptible to the pathogen resulted in the accumulation of proteinase inhibitor I and II mRNAs in this organ. Our data showed that in the lines used in this study, proteinase inhibitor II mRNAs accumulated in leaves to higher levels than proteinase inhibitor I mRNA in response to P. s. pv. tomato infection and wounding. Proteinase inhibitor II mRNAs accumulated more rapidly in disease-resistant than in disease-susceptible plants. Proteinase inhibitor I mRNAs were first detected in the disease-susceptible line during infection and wounding. In contrast to wounding, the systemic induction of these genes during pathogen ingression was limited. These data show that the plant proteinase inhibitors constitute one of the components of the plant defense system that are induced in response to bacterial pathogen invasion.