In many areas of the world there is a geographically localized high incidence of alimentary and bladder cancer in cattle. Studies in western Scotland have demonstrated that this phenomenon is associated with ingestion of bracken fern. However, the affected animals and herds were shown also to have an unusually high infection rate of alimentary papillomas caused by a previously unrecognised bovine papillomavirus (BPV) and that these tumors could undergo malignant transformation. Long-term field and experimental studies were started and indicate that the pathogenesis of the tumours and their relationship to virus infection and food-derived mutagens is complex. Results from these studies, and from cellular and molecular biology experiments, are presented and discussed in the context of recent papillomavirus findings in the human subject.