Chinese hamster ovary (CHO) strain 10215 carries a dominant mutation which confers resistant to cAMP by virtue of an altered catalytic subunit of the CAMP-dependent protein kinase (Evain et al., 1979). This mutation was transferred to wild-type CHO cells by DNA-mediated gene transfer. Based on the absence of cAMP growth inhibition, seven transformant colonies were isolated. One of these, 11586, was studied in detail. This transformant showed t h e same phenotype as the mutant, including resistance to the morphological changes and growth inhibitory effects of 1 mM 8-Br-cAMP, reduced total cAMP dependent protein kinase activity and lowered sensitivity of the kinase to cAMP activation. When the CAMP-dependent protein kinase was fractionated on a DEAE-cellulose column, the transformant was lacking in type I1 cAMP dependent protein activity, to the same degree as the mutant. The transformant and mutant, but not wild-type cells, also failed to phosphorylate a 52,000-dalton protein in a CAMP-dependent manner. These characteristics support the conclusion that the gene for the mutant CAMP-dependent protein kinase has been transferred. The ability to transfer this gene by DNA-mediated transfer suggests that this methodology may be useful for the molecular isolation of the gene encoding the catalytic subunit of CAMP-dependent protein kinase.