The SWI/SNF complex is an ATP-dependent chromatin remodeling complex that plays an important role in the regulation of eukaryotic gene expression. Very little is known about the function of SWI/SNF complex in plants compared with animals and yeast. SWI3 is one of the core components of the SWI/SNF chromatin remodeling complexes in yeast. We have identified a putative SWI3-like cDNA clone, CHB2 (AtSWI3B), from Arabidopsis thaliana by screening the expressed sequence tag database. CHB2 encodes a putative protein of 469 amino acids and shares 23% amino acid sequence identity and 64% similarity with the yeast SWI3. The Arabidopsis genome contains four SWI3-like genes, namely CHB1 (AtSWI3A), CHB2 (AtSWI3B), CHB3 (AtSWI3C) and CHB4 (AtSWI3D). The expression of CHB2, CHB3 and CHB4 mRNA was detected in all tissues analyzed by RT-PCR. The expression of CHB1 mRNA, however, could not be detected in the siliques, suggesting that there is differential expression among CHB genes in different Arabidopsis tissues. To investigate the role of CHB2 in plants, Arabidopsis plants were transformed with a gene construct comprising a CHB2 cDNA in the antisense orientation driven by the CaMV 35S promoter. Repression of CHB2 expression resulted in pleiotropic developmental abnormalities including abnormal seedling and leaf phenotypes, dwarfism, delayed flowering and no apical dominance, suggesting a global role for CHB2 in the regulation of gene expression. Our results indicate that CHB2 plays an essential role in plant growth and development.