The amount of cytomegalovirus (CMV) DNA in the blood (CMV load) may be a marker for detection of resistant CMV.METHODS. A total of 165 patients with AIDS and CMV retinitis had CMV load measurements (plasma and leukocyte) and cultures performed every 3 months; these measurements were correlated with CMV resistance to antiviral drugs and CMV retinitis progression (from masked readings of retinal photographs).RESULTS. Detectable plasma and leukocyte CMV loads were associated with CMV retinitis progression (odds ratios [OR], 6.3; P<.0001 and OR, 6.6; P<.0001, respectively), phenotypic resistance (OR, 6.1; P<.0001 and OR, 23.4; P=.0002, respectively), and genotypic resistance (OR, 17.5; P<.0001 and OR, 51.6; P=.0004, respectively). The sensitivity, specificity, and positive and negative predictive values of plasma CMV loads were 0.47, 0.86, 0.36, and 0.91, respectively, for progression and 0.59, 0.81, 0.07, and 0.99, respectively, for resistance; those of leukocyte CMV loads were 0.52, 0.83, 0.35, and 0.91, respectively, for progression and 0.82, 0.78, 0.08, and 0.99, respectively, for resistance. A detectable plasma CMV load at the time of diagnosis of CMV retinitis was associated with mortality (median survival time, 13.6 vs. 29.7 months; P=.007).CONCLUSIONS. CMV load has limited clinical utility, because of its low positive predictive value. Its high negative predictive value for occurrence of resistant CMV suggests that it may have utility as a screening tool to exclude resistance.