Protein kinase CK2 seems to play an essential role in cellular growth regulation as well as in apoptosis. By using a pair of prostate carcinoma cell lines which are either hormone-sensitive (LNCaP cells) or hormone-refractory (PC-3 cells) we analysed the contribution of protein kinase CK2 to their different growth behaviour as well as to apoptosis. We found the same amount of CK2 subunits in both cell lines although the enzymatic activity of CK2 was much higher in the hormone-refractory cells. These results for the first time show a correlation between the specific activity of protein kinase CK2 and specific growth properties of prostate cancer cells. The antiproliferative flavonoid apigenin led to an inhibition of the CK2 activity in both types of cells but only the hormone-sensitive LNCaP cells responded with apoptosis. Thus, these results demonstrate that a high CK2 activity is dispensable for growth and not necessary for a protection against apoptosis in hormone-refractory prostate cancer cells.