Different evidence suggests that VIP has immunoregulatory functions and may be secreted by different cells involved in inflammatory and immune responses. In the present study, we demonstrate by reverse transcription (RT) and polymerase chain reaction (PCR) VIP gene expression in rat thymocytes and T and B cells derived from spleen and lymph nodes. We have obtained a specific VIP cDNA product of 458 bp identical in size to that obtained from cerebral cortex. These results have been confirmed by Southern blot analysis. VIP message has also been detected in the T-T hybridoma YH-1633 and in a non-immune cell line, the pheochromocytoma PC 12. VIP gene expression in central and peripheral lymphoid organs suggests that VIP may be a T and B cell-derived cytokine involved in T-cell differentiation and in cell immune responses.