Internationally there is a correlation between the mortality-rates for colon cancer and coronary heart-disease. Dietary fat is suspected as a common ætiological factor, perhaps operating in colon cancer through the transformation of bile-salts into carcinogens by certain intestinal bacteria. This evidence prompts a search for associations between the two diseases within individual populations, and the present report analyses the relation between blood-cholesterol level and the development of colon cancer. Data from six prospective studies of coronary heart-disease in men have been pooled, yielding 90 cases of colon cancer. The initial levels of blood-cholesterol in these men were found surprisingly to be lower than the expected values, the median deviation being -0·26 standard-deviation units (corresponding to a little more than 10 mg. er 100 ml.), p<0·05. This tendency was not significantly correlated with the interval from screening to death, nor was it shared by cases of other alimentary carcinomas.