Forty-three blood samples from atherosclerotic donors and 28 samples from normal individuals were analyzed to determine the frequency of occurrence of cytomegalovirus (CMV) and Chlamydia pneumoniae DNA sequences in lymphocytes of Saudi Arabian donors using Polymerase Chain Reaction (PCR). In non-atherosclerotic donors, no CMV DNA was detectable and only one sample was positive for C-pneumoniae DNA sequences. Of the 43 atherosclerotic patients, 22 were infected with CMV, 23 were infected with C-pneumoniae and 11 showed no infection. Thirteen of the 43 donors showed simultaneous infection with both CMV and C-pneumoniae. These results demonstrate that atherosclerotic patients are more frequently infected with CMV or C-pneumoniae or both.