Previously we demonstrated that C3H1OT½ murine fibroblasts overexpressing avian c-src exhibit elevated levels of cyclic AMP (cAMP) in response to 13-adrenergic believed to be important for signalling processes. In this study we show that the sites of phosphorylation by protein kinase C (PKC) (Ser-12 and Ser-48) as well as the SH2 region of pp60C are required for the enhanced response of c-src overexpressors to 13-agonist stimulation. Mutation at the site of myristylation (Gly-2) results in a decrease in the enhanced response, while mutation at the site of phosphorylation by cAMP-dependent protein kinase (Ser-17) has no effect. Two-dimensional phosphotryptic analyses indicate that phosphorylation on Ser-12 and Ser-48 in unstimulated cells is associated with the ability of overexpressed pp60csrc to potentiate 13-adrenergic signalling. Cells overexpressing wild-type c-src also exhibit enhanced cAMP accumulation upon treatment with cholera toxin, an effect that is abated in cells overexpressing pp60`c