B and T cells develop following a similar early stepwise progression to later stages where multiple developmental options are available. These developmental regimes necessitate differential gene expression regulated by a large number of transcription factors (TFs). The resultant burgeoning amount of information has opened a knowledge gap between TF activities during lymphocyte development and a researcher's experiments. We have created the LymphTF database (DB) to fill this gap. This DB holds interactions between individual TFs and their specific targets at a given developmental time. By storing such interactions as a function of developmental progression, we hope to advance the elucidation of regulatory networks that guide lymphocyte development. Besides queries for TF-target gene interactions in developmental stages, the DB provides a graphical representation of downloadable target gene regulatory sequences with locations of the transcriptional start sites and TF-binding sites. The LymphTF-DB can be accessed freely on the web at