1. Kinetic and immunological studies as well as electrophoretic behaviour indicated that pyruvate kinase in Reuber H35 hepatoma cells is of the M2-type. 2. Addition of 0.1 microM insulin or 2 mM fructose to the incubation medium for 72 hr increased the activity of the M2-type pyruvate kinase in Reuber H35 hepatoma cells by 103 and 25% respectively. 3. Incorporation studies with [3H]leucine followed by immunoprecipitation showed that the apparent rate of synthesis of the M2-type pyruvate kinase was increased by both insulin and fructose. 4. Degradation studies indicated that the addition of insulin and fructose to the incubation medium increased the half-life of the M2-type pyruvate kinase from 4.8 to 8.6 and 6.8 hr respectively.