The immunogenic potential of Vibrio cholerae ghosts (VCG) in comparison with heat-killed whole-cell vibrios (WCV) was evaluated after intraperitoneal immunization of adult mice. Swiss white mice received four doses of VCG or WCV intraperitoneally, consisting of 500 micrograms of lyophilized material in 200 microliters of phosphate-buffered saline (PBS), pH 7.4. The control group received 200 microliters of PBS. Serum samples were collected from all mice on the day of immunization and on days 14, 24, 35 and 62 postimmunization. Sera were examined for vibriocidal antibodies by the microtitre and tube-dilution methods and Vibrio-specific serum IgG antibodies were assessed by ELISA. IgG antibodies to intact WCV were detected in sera from all animals immunized with VCG or WCV. The response was specific and of high magnitude. Significantly higher antibody responses were obtained when sera from both VCG- and WCV-immunized mice were titrated against VCG. The immunogenicity of VCG in evoking serum IgG responses was higher than that of WCV. However, the immunogenicity of the two antigen preparations was comparable in terms of seroconversion for vibriocidal antibodies. These results demonstrate that VCG administered intraperitoneally evoke Vibrio-specific serum IgG responses as well as vibriocidal antibody activity in mice.