The role of enhanced anaerobic glycolysis in the transformation of human peripheral lymphocytes induced by mitogens has been investigated. The DNA syntesis, lactate production and increment of lactate dehydrogenase isoenzyme 5 (LDH5) have been studied. In this paper we present detailed kinetic studies, which indicate that LDH5 increment correlates closely with rapid synthetic activity and is not morely part of an overall increase in enzymatic activities.