Forty-three persons chronically exposed to vinyl chloride were examined. In their blood serum activity of AlAT and AspAT aminotransferases, alkaline phosphatase, concentration of total protein and electrophoretic fraction, thymol test value, concentration of ferrum, latent and total ability of ferrum binding, and transferrin ferrum saturation coefficient were determined. In addition, determined were bromsulphtaleinic test and J-131 labelled Bengal red test; furthermore, protein synthesis index was determined, using the Se-75 labelled selenemethionine. The test group, as compared to correct values, exhibited a significant increase in Fe concentration in serum, significantly prolonged Bengal rose decay halftime in blood, and statistically significant decrease in the rate of plasma protein synthesis. The greatest percentage of pathological results was that of the index of protein synthesis rate (50%), T1/2 of CBJ-131 activity decay (39.5%), transferrin ferrum saturation coefficient (30.4%), concentration of Fe (26.1%) and gammaglobuline (24.3%) in serum. A considerable part of the reduced protein synthesis index in the test group of workers pointed to its usability for detecting early disturbances in liver functioning.