Although decreasing in most parts of the world, gastric cancer is still a major cause of cancer mortality, being the third commonest fatal cancer in the UK and the commonest site in much of Eastern Asia, and South and Central America. It has a poor prognosis, partly because the diagnosis is usually made too late and it does not respond well to treatment. Consequently there is a lot of interest in determining the cause of the disease and the means of its prevention or early diagnosis. Within the UK there is considerable regional variation in the incidence of gastric cancer (Chilvers & Adelstein, 1980); in general the incidence is lowest in the south and east of England and highest in Wales, Scotland and Northern Ireland. Amongst the many histopathological classifications, that described by Lauren (1965) has proved to be of particular interest to those studying the aetiology of the disease. On the basis of their histology and cytology, secretion of mucin and mode of growth, he divided gastric cancers into two main typesintestinal and diffuse (Table I, Figure 1), and studies by Correa (1981) and others have indicated that the intestinal type is caused by environmental factors whilst the diffuse form has a genetic predisposition. The evidence for this was reviewed recently by Lehtola (1978). Intestinal type gastric cancer predominates in areas with a high incidence of the disease, and populations which moved from a high to a low incidence area experienced a decline in the incidence of intestinal type gastric cancer, whilst the number of diffuse type cancers remained unchanged. At the family level Kekki et al. (1975) found that the first degree relatives of patients with diffuse gastric cancer are liable to develop atrophic gastritis. Anecdotal reports from pathologists in North Wales suggested that gastric cancer in this region was almost always of the diffuse pattern, indicating that this local high incidence of gastric cancer was Table I A comparison of the characteristics of diffuse and intestinal type gastric cancers (Summarised from Lehtola, 1978)