A study on the distribution of ABO blood groups was carried out on 85 patients with clinically and bacteriologically proven shigellosis. A significant association (P less than 0.01) of blood group B was observed with shigellosis cases in comparison to controls from whom no Shigella species or other enteropathogen could be isolated. Patients with isoagglutinin B or those who possess blood group B antigen may be at a relatively increased risk of shigellosis.