Shigella live vaccine was applied orally, four or five times, to 12000 children, aged between one and seven years. Morbidity in the immunised group was 3.5 times as high (9.3 times after boostering) as that in the non-immunised control group. Immunity could be provided for four months, and it was strictly specific of types. Results so far obtained from animal experiments, such as pulmonary and kerato-conjunctival tests on mice, are likely to support the idea of developing a combination vaccine from streptomycin-dependent Sh. flexnerica and Sh. sonnei mutants. Oral immunisation of mice, using 0.25 mg of dissolved Salmonella (S.) typhimurium antigen provided protection for all animals that had been exposed to 150 times of LD50, while 70 per cent of the mice involved still were protected by one tenth of that dose. More mutants will be tested (Shigella; S. enteritidis; S. typhimurium), and the expected results may give a foundation on which to devise effective vaccines.