The paratyphoid Salmonella bacteria, comprising more than 2,000 serovars or serotypes, are a major problem to the poultry industry. This is largely the result of entry of the bacteria into the human food chain. Human infection takes the form of a gastroenteritis, which in highly susceptible individuals can result in death. Some strains of certain serotypes have the capacity to produce morbidity and mortality in very young chickens. In adult birds, some serovars become localised in the reproductive tract with concomitant vertical transmission. The association between S. Enteritidis and table eggs has produced a great deal of publicity and concern with resulting national and international attempts at controlling the major serotypes, S. Typhimurium and S. Enteritidis, at the breeder and layer level. Control is possible through rigorous hygiene and management procedures, but is not always economically viable. As a result, control by serological and bacteriological testing and slaughter may also not be feasible. Antibiotics have been used to reduce carriage but can cause problems of resistance and increased susceptibility. The use of growth promoting antibiotics can also increase susceptibility to infection. Other means of increasing the resistance of poultry to infection are therefore being sought. These include the use of intestinal flora preparations for competitive exclusion of Salmonella from newly hatched chicks. Killed and live vaccines are used, both with some success. However, the safety of some live vaccines is still uncertain.