Prevalence rates for three hepatitis B virus (HBV) markers in two groups of personnel within the Canadian Armed forces (1848 incoming recruits and 210 crew members from a destroyer) were determined. Blood specimens for analysis were provided twice. The initial prevalence rates fell at the lower end of the spectrum when compared with those found in United States military personnel, Canadian military health personnel, and certain Canadian civilian populations. Eleven recruits and one destroyer crew member seroconverted for at least one of the markers between the first and the second testing. Their serological profiles are discussed in detail. No transmission of HBV between individuals in the group of recruits studied was established. However, evidence was found for a probable limited transmission of HBV between two crew members of HMCS Margaree. These findings combined with the high cost of the hepatitis B vaccine indicate that mass immunization for HBV in the Canadian Forces population cannot be justified on the basis of this study.