A study of the prediction of cancer and coronary heart disease on the basis of coffee consumption and personality shows that in cancer-prone probands (diagnosed on the basis of a personality inventory) coffee consumption was related to low incidence of cancer and high incidence of coronary heart disease, while diazepam showed the opposite trend. In coronary heart disease-prone probands coffee drinking was also linked with low incidence of cancer and high incidence of coronary heart disease, with diazepam again showing the opposite trend. In a personality type not prone to either disease, neither coffee consumption nor diazepam was linked with death from cancer or coronary heart disease. It is suggested that personality interacts in a predictable way with coffee and diazepam to determine in part the likelihood of death from cancer or coronary heart disease. Imipramine acts in a fashion similar to coffee, and opposite to diazepam.