Abstract Binding of 3′, 5′ cyclic AMP (cAMP) was investigated in view of the role of this nucleotide in the induction of enzyme secretion in the rat parotid gland. The experiments were carried out with the microsomal fraction which showed a high affinity for cAMP. Half maximal binding was obtained at 2×10 −7 M cAMP. N 6-monobutyryl cAMP which is an efficient inducer of enzyme secretion in the parotid gland inhibited the binding of 3H labeled cAMP more efficiently than any other nucleotide tested. Preincubation of the microsomes with either phospholipase C or trypsin caused a marked decrease in the amount of 3HcAMP bound/mg protein. Partial separation between smooth and rough microsomes indicates that the binding site for cAMP is localized preferentially in the smooth membranes.