It has been shown in vitro that bacteria are able to form or release carcinogens, mutagens, or promoters from intestinal secretions such as bile, or from excretions such as urine. It is, therefore, of interest to find out whether chronic infection of the gallbladder is associated with carcinogens, as in chronic infection of the urinary bladder. A study of cancer risk in chronic typhoid and paratyphoid carriers showed a large excess (observed/expected cases) for cancer of the gallbladder (167.0; 95% confidence interval 54.1-389) and also excess risks of cancer of the pancreas (8.1), colorectum (3.0), lung (2.5), and all neoplasms (2.6). There was no similar excess risk in a group of 386 people with typhoid from the 1964 Aberdeen outbreak. This indicates that it is long-term typhoid carriage, not acute infection, which is the risk factor. This has important implications for cancer prevention. Eradication of chronic carriage, by use of antibiotics or elective cholecystectomy, should be re-emphasised, and the need for good documentation of carriers is, therefore, of great importance.