Cytomegalovirus (CMV) infections in immunocompromised patients and congenital infections in infants have high morbidity and mortality while it may lead to asymptomatic infections in immunocompetent subjects. Serological tests, culture methods, antigenemia tests and molecular methods are applied in the diagnosis of CMV infection. The aim of this study was to investigate the presence of CMV in peripheral blood samples of patients who were at risk for CMV disease by shell vial cell culture, antigenemia test and real-time polymerase chain reaction (RT-PCR) methods. A total of 141 blood specimens obtained from 91 patients (33 female, 58 male) with suspected CMV disease were included to the study. Five of the patients were newborns and the others aged between 17-79 years old were bone morrow (n = 81), kidney (n = 4) and liver (n = 1) transplantation patients. Shell vial (Vircell, Spain) cell culture method was applied for CMV isolation from the samples, while the detection of pp65 antigen in blood leukocytes was investigated by indirect immunofluorescence method (CINAkit Argene, Biosoft, France). The presence of CMV DNA in plasma samples was detected by RT-PCR (CMV QNP 2.0 kit; Fluorion, Iontek, Turkey) method. CMV was found positive in 72 (51%) of 141 samples by shell vial, 82 (58.2%) by antigenemia test and 49 (34.8%) by RT-PCR. Considering cell culture as the gold standard, the sensitivity and specificity of antigenemia test were calculated as 81.9% and 66.6%, respectively; and for PCR those rates were 43% and 73.9%, respectively. In addition DNA sequencing (ABI Prism 310 Genetic Analyzer; Perkin Elmer, USA) was performed for the samples of randomly selected three patients out of 15, who were yielded positive results with cell culture and antigenemia tests but negative CMV DNA by RT-PCR. In this analysis CMV DNA was found positive in three of the samples that were found negative by RT-PCR in spite of CMV isolation and positive antigenemia. DNA sequencing of those samples revealed multiple mutations in the probe binding region (gB) of CMV QNP 2.0 kit. It was concluded that for the detection of CMV viremia and viral load in patients under risk for CMV disease, antigenemia and PCR based methods could be applied, however, negative results obtained by PCR targeting CMV gB gene, should remind the possible presence of mutations in the related site and the results should be confirmed by sequence analysis.