Expression of the genes coding for carbonic anhydrase in leaves of Arabidopsis thaliana, as induced by dehydration and osmotic stress (polyethylene glycol, PEG) was analyzed, and the activities of carbonic anhydrase were determined, using three accessions, Landsberg erecta (ler), Cape verde Islands (Cvi) and Antwerpen (An). Carbonic anhydrase activities and the expression of genes encoding carbonic anhydrases in Arabidopsis leaves had different responses to dehydration and to polyethylene glycol treatment. The expression of the gene coding for the chloroplastic form of carbonic anhydrase (ca1) was little influenced by the treatments, as compared to that for the cytoplamic form (ca2). The expression of the genes ca1 and ca2 in Ler accession was stable. The dehydration had little influence on the expression of ca1 and the carbonic anhydrase activities, and the osmotic stress induced by polyethylene glycol may decrease the expression of ca2 in Cvi and An accessions, and the carbonic anhydrase activities in all of accession. The results obtained from the present study can partly account for the difference of adaptation-drought mechanisms among the three accessions.