The authors investigated the activity of alkaline phosphatase, alanin- and aspartate-aminotransferases of the blood serum, mitochondria and postmitochondrial fraction of the liver in conditions of administration of mineral cotton from ferronnickel slag. It was shown that 1 and 3 months after introduction of mineral cotton dust changes occurred in the activity of these enzymes. Restoration of these enzymes occurred 6 months after introduction of mineral cotton dust.