A short heat pre-treatment (1 h at 38°C) was found to protect both suspension-cultured apple fruit cells and tobacco cells from cold-induced cell death. Tobacco cells were more sensitive to low temperatures than apple cells, with significant cell death after 48 h at 0 or –2°C. Real-time measurements of H₂O₂ levels during the heat pre-treatment revealed a substantial burst of this reactive oxygen species in both cell types. Real-time and longer-term measurements also showed a large burst of H₂O₂ production from tobacco cells, but not apple cells, when exposed to low temperatures. Lower temperatures reduced levels of peroxidase activity (both total and intracellular), with the heat pre-treatment preventing some of the cold-induced reduction of this activity in both apple and tobacco cells. The greater sensitivity to low temperature of the tobacco cells may be related to higher H₂O₂ production, with the heat treatment maintaining higher peroxidase activity. The lesser sensitivity of the apple cells may be due to the lack of a H₂O₂ burst and maintenance of peroxidase activity by the heat treatment. These results support a role for oxidative metabolism in the beneficial effects of heat in inducing low temperature tolerance.