We report here that the higher levels of calmodulin in transformed chicken embryo fibroblasts are due to an increase in the rate of synthesis of calmodulin that results from an increased amount of calmodulin-specific mRNA in transformed cells. Transformation of several types of eucaryotic cells by oncogenic viruses results in a two- to threefold increase in the intracellular levels of calmodulin. We used the normal chicken embryo fibroblast and its Rous sarcoma virus-transformed counterpart to examine the biosynthesis of calmodulin. We show that the higher levels of calmodulin found in transformed fibroblasts appear to be the consequence of a selective increase in the rate of synthesis of calmodulin above that of total soluble or total cellular protein. A significant difference in the rate of degradation of calmodulin or total protein between transformed and normal cells was not detected. We also examined the mechanism of the increased synthesis rate of calmodulin and show that the levels of calmodulin mRNA are increased in transformed fibroblasts as measured by both translational activity and hybridization to a calmodulin cDNA probe. It is suggested by these data that the higher levels of calmodulin in transformed cells may result from a specific increase in the rate of either calmodulin gene transcription or mRNA processing.