Characterization of T. vaginalis strains isolated from symptomatic and asymptomatic subjects was done by isoenzyme analysis. The pathogenicity of these isolates was checked in mouse model and in vivo drug susceptibility was determined. The isolates from symptomatic and asymptomatic individuals could not be grouped on the basis of isoenzyme analysis alone. All the strains except one, were pathogenic for mice, and metronidazole (50 mg/kg body weight) was effective in protecting the mice from T. vaginalis infection.