Comprehensive analysis of DNA-protein interactions is important for mapping transcriptional regulatory networks on a genome-wide level. Here we present a new application of mRNA display for in vitro selection of DNA-binding protein heterodimeric complexes. Under improved selection conditions using a TPA-responsive element (TRE) as a bait DNA, known interactors c-fos and c-jun were simultaneously enriched about 100-fold from a model library (a 1:1:20 000 mixture of c-fos, c-jun and gst genes) after one round of selection. Furthermore, almost all kinds of the AP-1 family genes including c-jun, c-fos, junD, junB, atf2 and b-atf were successfully selected from an mRNA display library constructed from a mouse brain poly A(+) RNA after six rounds of selection. These results indicate that the mRNA display selection system can identify a variety of DNA-binding protein complexes in a single experiment. Since almost all transcription factors form heterooligomeric complexes to bind with their target DNA, this method should be most useful to search for DNA-binding transcription factor complexes.