Rat cholecystokinin-B (CCK-B) receptors were transfected into Chinese hamster ovary (CHO)-K1 (CHO-CCK-B) and Swiss 3T3 (Swiss 3T3-CCK-B) cells, and the effects of receptor activation on cell proliferation and intracellular signaling were investigated. CCK octapeptide (CCK-8) treatment had no effect on cell growth in quiescent CHO-CCK-B cells but inhibited DNA synthesis, proliferation, and colony formation when the cells were grown in fetal bovine serum (FBS). In contrast, CCK-8 stimulated DNA synthesis in quiescent Swiss 3T3-CCK-B cells and had no effect when the cells were grown in FBS. These differences in growth responses were not due to differences in the level of receptor expression, as similar numbers of receptors were present in both cell types. To determine whether the different growth effects were due to differences in receptor coupling to common second messenger pathways, we investigated the effects of CCK-8 on several known intracellular signals. In both cell types, CCK-8 stimulated increases in intracellular Ca²⁺ concentration and polyphosphoinositide hydrolysis with similar potencies and efficacies. CCK-8 also stimulated arachidonate release from both cell types, although the potency was higher in the CHO cells. Adenosine 3',5'-cyclic monophosphate generation was observed at high agonist concentrations in both cell types and was much greater in cells with higher receptor density. In summary, receptor activation had opposite effects on growth parameters in CHO and Swiss 3T3 cells, but only minor differences were observed in the characteristics of CCK-B receptor coupling to specific second messengers in the two cell types. Thus cellular context is a principal determinant of the biological effects of CCK-B receptor activation, and differences in biological responses may occur independently of major differences in receptor coupling.