Summary We demonstrate that the biophysical technique of surface plasmon resonance (SPR) analysis, which has previously been used to measure transcription factor binding to short DNA molecules, can also be used to characterize interactions involving entire gene promoters. This discovery has two main implications that relate, respectively, to novel qualitative and quantitative uses of the SPR technique. Firstly, SPR analysis can be used qualitatively to test the capacity of any transcription factor to interact physically with its putative target genes. This application should prove particularly useful for the confirmation of predicted transcriptional interactions in model species, and for comparative studies of non-model species in which transcriptional interactions are not amenable to study by other methods. Secondly, SPR may be used quantitatively to characterize interactions between transcription factors and gene promoters containing multiple cis-acting sites. This application should prove useful for the detailed dissection of promoter function in known target genes. The qualitative and quantitative applications of the SPR analysis of whole promoters combine to make this a uniquely powerful technique, which should prove particularly useful in systems biology, evolutionary developmental biology and various branches of applied biology.