An assay for quantitation of cytomegalovirus (CMV) has been developed. The assay combines DNA amplification and enzyme-linked immunosorbent assay (ELISA) detection. In this study, the assay has been used to examine sequential buffy-coats from 32 consecutive liver transplant recipients. In a febrile patient, CMV titres in excess of 10(4) copies per 150,000 cells strongly suggest a diagnosis of symptomatic CMV infection. Antiviral therapy causes a rapid decline in viral titre. Viral titres are seen to rise presymptomatically in some patients. Median peak viral titres differ significantly between symptomatic patients (1.1 x 10(5)), asymptomatic CMV IgM-positive patients (1.7 x 10(3)), and asymptomatic CMV immunoglobulin (Ig)M-negative patients (2.9 x 10(2)). CMV quantitation can be used for diagnosis and surveillance and can also be used to monitor antiviral treatment.