BACKGROUND Centrifugation shell vial (SV) and conventional tube culture (TC) are the most common methods for detecting cytomegalovirus (CMV) viremia. Studies have indicated that SV is more sensitive than TC but at least one report suggested that TC was more sensitive. Because CMV in the blood is primarily associated with infected leukocytes, the number of leukocytes inoculated into the different culture systems could affect the sensitivities of the two systems. OBJECTIVE To compare the sensitivities of SV and TC for detection of CMV viremia by inoculating equal numbers of leukocytes into paired SV cultures and TC cultures. METHODS Leukocytes from transplant recipients were isolated and counted. Equal numbers of leukocytes were then inoculated into each of two MRC-5 SV and into each of two MRC-5 TC. SV was considered positive when either one or both vials were positive, and TC was considered positive when either one or both tubes showed evidence of CMV cytopathic effect (CPE). RESULTS From a total of 434 specimens tested, 85 (19.6%) were positive by SV or TC. CMV was detected by SV in 75 (88%) of the positive specimens, compared to TC which was positive in 40 (47%) of the positive specimens. CONCLUSIONS When equal numbers of leukocytes were inoculated into each system, SV had significantly greater sensitivity than TC for detecting CMV viremia. However, a small number of episodes of viremia were detected only by TC. Therefore, both methods should be used for maximum sensitivity.