Abstract Inoculation of three leaves of tobacco cv. Ky 14 with tobacco mosaic virus and incubation at 23 °C for 3–12 days caused localized necrosis on the inoculated leaves whereas plants held at 28 °C after inoculation developed systemic mosaic symptoms. Pathogenesis-related (PR) proteins and activities of peroxidase, β-1,3-glucanase and chitinase systemically increased in the inoculated plants at 23 °C. When TMV-inoculated leaves were removed 12 days after inoculation at 23 °C and plants were challenged with TMV or Peronospora tabacina and held at 23 °C, induced resistance to P. tabacina and TMV was apparent. However, resistance to blue mould but not TMV was apparent when the procedure was repeated, except that plants were transferred to 28 °C one day after challenge with TMV or P. tabacina. PR proteins and activities of peroxidase, β-1,3-glucanase and chitinase were further increased after challenge with P. tabacina or TMV in induced plants at both temperatures. Tn 86, a cultivar systemically susceptible to TMV, was protected against blue mould but not against TMV by stem inoculation with P. tabacina. PR proteins were induced and the activities of peroxidase, β-1,3-glucanase and chitinase were greatly increased in the induced plants.