The effect of excess copper on the expression of soluble proteins in 10-day old Phaseolus vulgaris seedlings was studied with two-dimensional electrophoresis and mass spectrometry, to find sensitive biochemical markers of exposure. Despite major differences in root Cu contents, both 15 and 50 microM Cu treatments resulted in equal enhancements of Cu in the primary leaves. Three proteins, apparently reacting in a dose-dependent manner to Cu exposure, were identified from roots. The levels of an intracellular pathogenesis-related protein and a newly identified protein homologous to PvPR1, PvPR2, were increased with increasing Cu concentration. The level of a newly identified PR-10 protein decreased in a dose-dependent manner. No significant difference was observed in the leaf protein pattern between controls and 15 microM Cu-treated plants. However, at 50 microM Cu exposure, the appearance of PvPR1 and a homologue of Arabidopsis thaliana thylakoid lumenal 17.4kDa protein was observed. Another protein slightly enhanced by Cu treatment had sequence homology to a mitochondrial precursor of glycine cleavage system H protein of Flaveria pringlei.