The clinical and immunological responses to typhoid vaccination with parenteral and oral vaccines in two groups of 30 adult male subjects were studied. Specific anti-Salmonella typhi cell-mediated immunity and total or specific anti-lipopolysaccharide faecal immunoglobulin (Ig) A titres in vaccinated subjects were monitored. Cellular antibacterial activity was significantly increased only in orally vaccinated subjects. Serum arming activity and inhibition experiments suggested an IgA-dependent cellular cytotoxicity in those orally vaccinated. In these subjects, a total and antilipopolysaccharide faecal IgA increase was observed lasting up to 8 months after completion of the vaccination schedule. In parenteral vaccinated subjects, an early onset transitory increase of IgM rheumatoid factor was observed. Oral vaccine was well tolerated and free of side effects, whereas 65% of parenterally vaccinated subjects reported side effects such as fever, headache, malaise and local tenderness in the injection site.