A quantitative culture method was used to test serial blood specimens from 28 lung transplant recipients at risk of cytomegalovirus (CMV) infection (donor [D] or recipient [R] seropositive for CMV). Viremia occurred in 26 (93%) of 28 patients. Highest levels were seen when the donor was seropositive. The median of individual maximum levels was 2.13 infectious centers (ICs)/10s leukocytes for D+/R· patients (interquartile range [iqr], 0.12-21.77), 1.01 for D+/R+ (iqr, 0.32.32), and 0.10 for D·/R+ [iqr, 0.07-0.36; P =.030, Kruskal-Wallis test). Higher levels were seen in patients with biopsy-proven CMV pneumonitis compared with those with negative biopsies (mean, 0.24 [SD 0.51] ICs/105 leukocytes vs. 0.01 [SD 0.03]; P =.039, Wilcoxon test) and with symptomatic CMV episodes compared with asymptomatic episodes (median, 0.34 ICs/I0s [iqr, 0.11-0.61] vs. 0.08 ICs/105 [iqr, 0.03-0.13]; P =.045, Wilcoxon test). Further studies are required to determine whether quantification of CMV viremia by this method will be of practical value in the recognition of significant CMV infection in lung transplant recipients.