Dimethoxy-2-nitrobenzyl adenosine-3′,5′ cyclic monophosphate (DMNB) is a metabolically active, photolabile cyclic AMP analog that yields free cyclic AMP upon UV hydrolysis. The analog is useful in that it permits short term, transient elevations of intracellular cyclic AMP. Addition of DMNB (1-10 μM) to mouse mammary epithelial cells, followed by UV irradiation of cells, caused a significant increase in DNA synthesis over that observed with controls, UV irradiation alone or DMNB alone. In subsequent studies, DMNB exhibited a modest, but statistically significant, interaction with epidermal growth factor in promoting DNA synthesis. Effects of DMNB were observed if DNA synthesis was measured as either 3H-thymidine incorporation into DNA or as percent S-phase cells. These results indicate that previously observed effects of agents such as cholera toxin and phosphodiesterase resistant cyclic AMP analogs on mammary epithelial proliferation can be mimicked, at least in part, by a short term pulse of cyclic AMP.