Transgenic tobacco seedlings that overexpress a cDNA encoding an enzyme with both glutathione S-transferase (GST) and glutathione peroxidase (GPX) activity had GST- and GPX-specific activities approximately twofold higher than wild-type seedlings. These GST/GPX overexpressing seedlings grew significantly faster than control seedlings when exposed to chilling or salt stress. During chilling stress, levels of oxidized glutathione (GSSG) were significantly higher in transgenic seedlings than in wild-types. Growth of wild-type seedlings was accelerated by treatment with GSSG, while treatment with reduced glutathione or other sulfhydryl-reducing agents inhibited growth. Therefore, overexpression of GST/GPX can stimulate seedling growth under chilling and salt stress, and this effect could be caused by oxidation of the glutathione pool.