Disruption of the oral mucosal lining and the lack of normal defense mechanisms predispose bone marrow transplant (BMT) patients to life-threatening infections, often caused by oral flora. Chlorhexidine, used as an oral antiseptic, appears promising in limiting oral bacteria and fungi, and therefore, may decrease oral complications associated with BMT. The purpose of this study was to determine in pediatric BMT recipients if a 0.12% chlorhexidine mouthrinse, used as an adjunct to normal in-hospital oral care regimens, would decrease the severity of oral mucositis as measured by oral ulcerations, bacteremia, and length of hospital stay. Forty-seven pediatric BMT subjects were included in this double-blind study. Subjects were instructed to use 15 ml of a mouthrinse 3 times daily to be swished and gargled for 30 sec. Each subject had 7 oral sites scored for the percentage of ulcerated mucosa twice weekly until day +35 or hospital discharge or death. Blood was cultured daily during neutropenia. Additionally, the number of days from onset of cytoreduction to hospital discharge or death was recorded for each subject. Alpha was set at .05. There was no significant difference in the severity of oral ulceration between the chlorhexidine and placebo groups (P = .18). Chlorhexidine did not reduce the development of bacteremia (P greater than .5), nor did it significantly decrease the length of hospital stay (P = .68).(ABSTRACT TRUNCATED AT 250 WORDS)