Cyclic adenosine monophosphate (cAMP) inhibits phorbol 12-myristate 13-acetate (PMA)-induced IL-2 production while it inhibits IL-5 production at the transcriptional level in EL-4, a mouse lymphoma line. The –321 to +46 region of the mouse IL-2 promoter is required for activation by PMA and inhibition by cAMP. This promoter region contains several elements that interact with transcription factors, such as nuclear factor of activated T cells (NF-AT), NF-κB, AP-1, and octamer. With use of reporter plasmid carrying multiple copies of each element, we found that the construct that contained the NF-AT site was most effective for responding to PMA activation and cAMP inhibition. In electrophoretic mobility shift assay (EMSA), PMA-induced NF-AT binding complex was altered by cAMP. Furthermore, overexpression of the cytoplasmic component of NF-AT abrogated the inhibitory action of cAMP. These results indicate that the NF-AT site is a target of the inhibitory action of cAMP. We have previously reported that the -1200 to +33 region of the mouse IL-5 promoter can mediate transcriptional stimulation by PMA and cAMP in EL-4 cells. Here we identified the element IL-5P, which is required for maximal activation of the IL-5 promoter. We found that this element is homologous to the binding site for NF-AT and interacted with NF-AT-related factors induced by PMA and cAMP. Thus it appears that an NF-AT factor is involved in the regulation of IL-5 gene transcription. (J ALLERGY CLIN IMMUNOL 1995;96:1126-35.)