Eukaryotic elongation factor eEF-2 mediates regulatory steps important for the overall regulation of mRNA translation in mammalian cells and is activated by variety of cellular conditions and factors. In this study, eEF-2 specific, Ca 2+ /CaM-dependent protein kinase III (CaM PK III), also called eEF-2 kinase, was examined under oxidative stress and cell proliferation state using CHO cells. The eEF-2 kinase activity was determined in the kinase buffer containing Ca 2+ and CaM in the presence of eEF-2 and [γ-32 P] ATP. The eEF-2 kinase activity in cell lysates was completely dependent upon Ca 2+ and CaM. Phosphorylation of eEF-2 was clearly identified in proliferating cells, but not detectable in CHO cells arrested in their growth by serum deprivation. The content of the eEF-2 protein, however, was equivalent in both cells. Using a phosphorylation statespecific antibody, we show that oxidant such as H 2 O 2 , which triggers a large influx of Ca 2+