IgE antibodies to the antiseptic agent chlorhexidine have recently been detected in the majority of sera from a small group of predominantly Japanese individuals showing anaphylactic-type adverse reactions towards chlorhexidine. In this study the prevalence of IgE and IgG antibodies with specificity for chlorhexidine was investigated in groups of Japanese and British individuals. The RAST data, using a better defined semi-chlorhexidine-HSA antigen than previously employed, revealed that chlorhexidine-specific IgE was only detected in Japanese individuals who had experienced anaphylactic-type reactions and was not detected in groups of Japanese nurses and patients, or in groups of British nurses and hospital staff, all in regular contact with chlorhexidine. A group of British blood donors was also negative. In contrast, IgG antibodies were detected not only in sera from chlorhexidine-sensitive Japanese patients, but also in several sera from Japanese nurses, non-sensitive Japanese patients and several British individuals. The possible reasons for these observations are discussed.