In bone marrow transplantation (BMT), cytomegalovirus (CMV) interstitial pneumonitis (IP) is one of the most dangerous complications, which has been the first important cause to lead the failure of BMT. At present, there is no effective and specific therapy for CMV-IP, therefore how to prevent CMV infection effectively is a top task. From 1991 to 1996, we used comprehensive steps to prevent CMV-IP in BMT, and none of 14 patients developed CMV-IP. The preventing results that we achieved by using the steps were quite satisfied.