In addition to an essential role in plant development, brassinosteroids (BRs) appear to have the ability to protect plants against various environmental stresses. However, studies confirming the ability of BRs to modulate plant responses to different environmental stresses are lacking. Earlier we had demonstrated that treatment with 24-epibrassinolide (EBR), a BR, increases the basic thermotolerance of Brassica napus and tomato seedlings [Plant Mol Biol 40:333-342, 1999]. Here we demonstrate that EBR treatment enhances seedling tolerance to drought and cold stresses in both Arabidopsis thaliana and B. napus, and helps to overcome a salt-stress-induced inhibition of seed germination. The ability of EBR to confer tolerance in plants to a variety of stresses was confirmed through analysis of expression of a subset of drought and cold stress marker genes. Transcriptional changes in these genes were more apparent in EBR-treated A. thaliana, in particular during earlier time points of stress. To see if BR is essential for the heat stress (HS) response, we made use of BR-deficient mutants. Both det2-1 and dwf4 mutants still expressed heat shock proteins (hsps) to high levels during HS, indicating that although BR augments thermotolerance in plants, it is not necessary for hsp expression during HS.