Cytoenzymochemical investigations were performed on the leukocytes and platelets from 2,782 workers occupationally exposed to benzene, vinyl chloride or carbon disulphide, in view of detecting the eventual occurrence of cytologic metabolic disorders induced by these chemical substances. The cytomorphologic aspects and the cytoenzymochemical parameters studied, such as the leukocyte alkaline phosphatase, endolymphocytic glycogen, lymphocytic nucleolar RNA amounts (revealed by the lymphocyte nucleologram), as well as the platelet counts have shown some abnormal values, whose severity was related to the time of exposure to toxic chemicals. The results obtained demonstrate the utility of such tests for an early detection of some metabolic disorders of the endolymphocytic proteins, carbohydrates or lipids, in view of preventing the occurrence of more severe pathologic consequences.