1. During the years 1954–56 large number of salmonellae, comprising six sero-types and a number of Salm. typhi-murium phage types, were isolated at the Bradford abattoir.

2. Most of the cultures were derived from pigs; the animals presented no sign of clinical illness.

3. Human salmonella infections in Bradford over the same period were closely related to the abattoir findings.

4. It seems probable that individual pigs are infected on the farms and when brought to the abattoir may infect others in the lairages.

5. Limiting the duration of stay in the lairages and prevention of overcrowding may substantially reduce the proportion of animals found infected at slaughter.

We wish to express our thanks to Dr John Douglas, Medical Officer of Health, Bradford, for his interest and encouragement in this investigation and to Mr F. H. Myres, Mr J. Noble, Mr E. Root and Mr R. Butterfield of the Bradford Health Department for their enthusiastic help. Thanks are also due to Dr Joan Taylor and Dr E. S. Anderson and staffs of the Salmonella and Central Enteric Reference Laboratories, Colindale, for their assistance in typing Salmonellae, and to a number of our colleagues who have kindly read the script and offered valuable criticisms.