A prospective cohort research revealed an increased morbidity level among oil-processing workers with chronic pretumour diseases (chronic bronchitis, anacid gastritis, ailments of the larynx and skin, diseases of cervix uteri, benign tumour of the uterus and pretumour mammary gland diseases). Statistically reliable data have been received with regard to lung cancer mortality of males in the sample cohort, and lung and cervix uteri cancer mortality of females, as well as the risk factors of lung, larynx and skin cancer in males, and lung and large intestine cancer in females,--all in comprison with workers who have no contact with oil-processing products.