The SWI/SNF complex is required for the enhancement of transcription by many transcriptional activators in yeast(1,2) Genetic and biochemical studies indicate that the complex facilitates activator function by antagonizing chromatin-mediated transcriptional repression(3-6). The absence of known DNA-binding motifs in several SWI/SNF subunits and the failure to identify SWI/SNF-dependent DNA-binding activities in crude yeast extracts have led to the belief that the complex does not bind DNA(7,8). Here we show that the SWI/SNF complex has a high affinity for DNA and that its DNA-binding properties are similar to those of proteins containing HMG-box domains(9). The complex interacts with the minor groove of the DNA helix, binds synthetic four-way junction DNA, and introduces positive supercoils into relaxed plasmid DNA. These properties are likely to be important in the remodelling of chromatin structure by the SWI/SNF complex.