Wild type and mutant Arabidopsis thaliana plants were used to investigate the protein expression of plants exposed to elevated concentrations of aluminum. Plants were grown in a growth chamber at 25°C, 16-hour day, and 8-hour dark for eight weeks before subjecting them to different concentrations of AlCl₃ solution. Time course experiments showed that Arabidopsis plants respond to aluminum toxicity by altering their protein expression. Our data indicate that aluminum toxicity caused Arabidopsis plants to express a protein in the range of 97 kD, and a medium-molecular weight protein in the range of 45 kD. Our data also indicate that responses by Arabidopsis plants to Al toxicity are not similar to responses to stresses that cause the induction of HSP70.