Abstract 1. 1. Glycogenic capacities of two rat ascites hepatomas, namely, glycogen- deficient AH-130 and glycogen-rich AH-66F, were compared either at whole cell level with [14C]glucose as substrate or by studying the activity and properties of glycogen synthetase. 2. 2. With [14C]glucose as substrate, glycogen synthesis was initiated in the two hepatomas at comparable rates, but in AH-130 the rate decline as glycogen accumulated while in AH-66F the rate was little affected by cellular glycogen level. 3. 3. When 2 mM amytal was present, AH-130 failed to synthesize glycogen from glucose while AH-66F carried out this synthesis at substantial rates. In AH-66F, lower concentrations of amytal led to the stimulation of glycogen synthesis; similar effects were produced by rotenone or 2,4-dinitrophenol. 4. 4. In glycogen-rich AH-66F cells, about 90% of the glycogen synthetase was recovered in particular fraction in association with glycogen. The enzyme was totally in a glucose 6-phosphate-independent (I) form. These findings suggested that the glycogen-induced I to D (glucose 6-phosphate-dependent) conversion of glycogen synthetase, previously reported to occur in AH-130, might not operate efficiently in AH-66F.