The effects of alpha calcitonin gene-related peptide (alpha CGRP) and vasoactive intestinal peptide (VIP) on the proliferation of CD4 and CD8 T-murine lymphocytes were investigated. When stimulated by a combination of phorbol 12-myristate-13-acetate (PMA) and calcium ionophore (A23187), both neuropeptides in a range of 10(-7)-10(-10) M had an inhibitory effect on the proliferative response of unfractionated splenocytes as well as of purified CD4 and CD8 T lymphocytes. The inhibitory effect of these two neuropeptides was completely or partially blocked by the antagonists of CGRP and VIP receptors. CGRP8-37 and (p-Cl-D-Phe6, Leu17VIP, respectively. The inhibitory effects of each neuropeptide on purified T cells were observed within 4 h after PMA/A23187 activation and their inhibitory actions were correlated with a decrease of IL-2 production. In addition, the two neuropeptides in a range of 10(-7)-10(-10) M induced a rapid and dose-dependent increase in intracellular cAMP in CD4 and CD8 T cells. This suggests the involvement of this second messenger in the inhibitory effects of these two neuropeptides. Taken together these results show that CD4 and CD8 spleen cells represent at least two of the cellular targets for CGRP and VIP inhibition of proliferation mediated by the same type of mechanism.