Correlation between pyruvate and lactate contents as well as between enzymes participating in turnover of the substrates (pyruvate- and lactate dehydrogenases, alanine aminotransferase, pyruvate kinase) were studied in rat liver tissue simultaneously with tumor growth and intensive thiaminotherapy. Thiamine, administered into rats carrying carcinosarcoma Woker-256 at a daily dose 12.5 mg/kg body weight, exhibited the normalizing effect on activity of enzymes studied, on quantitative content of LDH isoenzymes and on content of lactate in blood and of pyruvate in liver tissue. Possible effect of thiamine on pyruvate metabolism in tumoral impairment is discussed.