The SMARCs (SWI/SNF-related, matrix-associated, actin-dependent regulators of chromatin), and BAFs (BRG1-associated factors), have been identified as components of the mammalian SWI/SNF-like chromatin-remodeling protein complexes. These multi-protein complexes are proposed to function as ATP-driven motors that translocate along DNA and destabilize nucleosomal structures to facilitate transcription factor binding. Two fractions of SWI/SNF-like complexes, SWI/SNF-A (BAF) and SWI/SNF-B (PBAF), have been isolated. The SWI/SNF-A (BAF) complex is defi ned by the presence of a BAF250/ARID1A subunit and either a SMARCA/BRG1 or SMARCA2/BRM subunit, while the SWI/SNF-B (PBAF) complex lacks the BAF250/ARID1A subunit and contains a SMARCA4/Brg1 subunit and a polybromo/BAF180 subunit. In addition to these defining subunits, the SWI/SNF-A (BAF) and SWI/SNF-B (PBAF) complexes possess multiple subunits of other SMARCs and/or BAFs that are present in various combinations to provide the mammalian cell with a functional variety of SWI/SNF-like chromatin-remodeling complexes. This growing family of interacting proteins has also been shown to associate with the N-CoR (nuclear receptor co-repressor) deacetylase complex and various nuclear transcription factors. Current information indicates an important role for these complexes in the regulation of cell growth and proliferation. Future studies will likely demonstrate that the SWI/SNF proteins are important to many aspects of development and tumorigenesis.