In a Yugoslav village, psychosocial, anamnestic medical, and pathophysiological data were recorded for 1,353 persons in a longitudinal study. The role of psychosocial stress in carcinogenesis, as far as we have investigated it, may be described as follows: (1) Psychosocial stress in terms of high hopelessness, high antiemotionality, etc. has a strong relevance for cancer incidence which does not act via one of our physiological variables associated with cancer. This follows from the results of our multivariate analysis. (2) Psychosocial stress is substantially associated with a low lymphocyte percentage, which in turn is a relatively strong risk factor for cancer. (3) Psychosocial stress is relatively weakly associated with the cholesterol minimum; but apart from the fact that the cholesterol characteristics of cancer subjects are more marked descriptively under stress conditions, psychosocial stress significantly enhances the efficacy of the most important physiological risk variables for cancer.