We found ten cases of human cytomegalovirus (CMV) infection who were intractable stridor. Their symptoms were not improved by the treatment with aminophyllin nor beta stimulants. They were admitted repeatedly complaining of stridor, fever and diarrhea. In two cases, the immunological findings showed a decrease of bacterial sterilizing activity of the neutrophils. Additionally, blood count showed leukocytosis more than 15,000/ul in all cases. Total serum IgE and specific IgE antibodies to many antigens were not elevated. Transaminase was elevated. Chest X-p findings of interstitial pneumonia or atelectasis continued for a long time in some cases. Virological examinations revealed high concentrations of specific IgM or CF antibodies against CMV in all cases. CMV DNA in saliva were examined by polymerase chain reaction (PCR) with primer sets for the immediate early (IE) region of CMV and showed positive in seven cases. CMV in bronchoalveolar lavage (BAL) was isolated in two cases, and CMV PCR in BAL was positive in three cases. The sequence of the CMV-PCR products showed almost same sequence except one point mutation in bp 1203. We considered that CMV infections in infants may induce stridor for a long period.