Objective To evaluate the clinical utility of CMV pp65 antigenemia by CMV brite Kit for predicting active/reactive CMV infection S as well as of CMV diseases in bone marrow or peripheral stem cell transplant patients. We also investigated the efficacy of preemptive therapy guided by detection of CMV antigenemia. Methods A total of 210 EDTA anticoagulant plasma samples from 36 bone marrow or Peripheral Stem Cell Transplant Patients were prospectively collected from September 1999 to April 2000. The specific CMV antibody IgG/IgM of all patients were detected by ELISA. We detected CMV pp65 antigenemia by indirect immunofluorescence assay using CMV Brite Kit. All blood samples were detected weekly from week 3 after bone marrow transplantation until 100 days or antigenemia turning negative/dischage or death. Ganciclovir preemptive therapy was initiated at first positive pp65 antigenemia. Results Of 36 bone marrow or Peripheral Stem Cell Transplant Patients, 16 patients occurred positive pp65 antigenemia, 15 patients suffered from symptomatic CMV infections or CMV diseases. In 14 patients of positive pp65 antigenemia receiving gaciclovir therapy at first antigenemia, 2 patients died (mortality rate 14.2%), 12 patients of pp65 antigenemia became negative. Otherwise, 2 untreated cases died. The study showed a significant difference in mortality rate between treated and untreated patients (P