Serological investigations for Campylobacter, Yersinia and Shigella in hospitalized children (different hospitals) in Iran revealed a contamination rate of 15% for Campylobacter, up to 19% for Yersinia and between 1 and 12% for the various strains of Shigellae. In diarrhoeal diseases the possibility of an infection with Campylobacter, Yersinia and Shigellae must be considered.