Nervous, endocrine, and immune systems share a large number of regulatory molecules including hormones and neuropeptides. Vasoactive intestinal peptide (VIP) plays an important role in a variety of immunological functions. In the present report, we sorted purified thymocytes of the four major thymic subsets defined by CD4 and CD8 phenotypes. We demonstrate by reverse transcription (RT) and polymerase chain reaction (PCR) both VIP and VIP1 receptor gene expression in double positive (CD4+CD8+) and single positive (CD4+CD8-, CD4-CD8+) thymocyte subsets. Double negative thymocytes (CD4-CD8-) lack VIP and VIP1 receptor gene expression.