Plants of two wheat cultivars (Triticum aestivum L., cultivars Mec and Chiarano), differing in sensitivity towards sulfur dioxide, were fumigated with 96 nL L-1 of SO2 for four months. Thylakoid membranes were subjected to two-dimensional electrophoresis in order to detect possible changes in the protein patterns. We found the greatest alterations following treatment in the polypeptide profiles of the most sensitive cultivar, Mec, even if some significant changes were also detected in the plants of the cultivar Chiarano.