The purpose of the work was to study the effect of benzene, toluene and xylene combined with acetone on ascorbic acid (AA) supply of constructive workers exposed to prolonged C-vitaminization. Vitaminization was carried out for 6 and 12 months with various doses of AA (50, 100 and 150 mg). Additional vitaminization induced a considerable increase in AA content in the blood plasma and raised its excretion with urine in the workers given 50 and 100 mg of vitamin C and not exposed to the harmful industrial factors. In painters working in the premises with an elevated content of aromatic hydrocarbons in the air, the higher level of AA in the blood plasma and urine could be attained only after prolonged additional vitaminization at a dose of 150 mg. The data obtained in experiments on guinea pigs also indicate advisability of increasing the daily preventive dose of vitamin C under industrial conditions with an elevated content of benzene and vapours of its methyl derivatives.