In this report we identify novel spliced forms of cyclic AMP (cAMP) response element-binding protein-1 (CREB-1) mRNA. These forms contained an additional 17 nucleotide insert, which we refer to as the β exon, located between exons 4 and 7 of the Δ, and 5 and 7 of the α forms of CREB-1 transcript (nomenclature of Ruppert et al. 1992; EMBO Journal 11, 1503-1512). The inclusion of the β exon led to the generation of mRNAs in which the frame of CREB-1 sequences 3′ to the exon was shifted such that the encoded proteins terminate after the transactivation domain, but before the target serine for cAMP-dependent protein kinase. The β exon-containing CREB-1 mRNAs were more abundant in tissues that respond poorly to cAMP, suggesting that the generation of βCREB-1 mRNAs may contribute to the down-regulation of CREB-1 activity and cAMP responsiveness.