This paper describes a novel method of behaviour therapy applied to cancer-prone and coronary heart disease-prone patients in a prophylactic manner, to reduce the probability of their dying of cancer or coronary heart disease. The treatment can also be applied to patients already suffering from cancer in order to prolong their lives. The methods used are described in considerable detail, together with the rationale leading to their adoption. In Part II of this paper are the results of several studies showing that the methods are surprisingly successful in preventing death in cancer-prone and coronary heart disease-prone probands, and prolonging life in patients already suffering from terminal disease.