On the basis of a study of 206 patients in conditions of in-patients services and 1124 patients in one of Moscow's district psychoneurological dispensaries it appeared possible to prove the significance of exogenous factors in the development of attacks in schizophrenia. The study did not show any significant differences in the frequency of combined attacks with exogenous factors depending upon the severity of schizophrenia. The frequency of attacks related to exogenous factors is in a direct dependence upon the existence or absence of exogenous factors in the manifest attack.