The glucose consumption rate of 9L rat brain tumor cells was determined as a function of concentration. Glucose uptake followed Michaelis‐Menten kinetics with a Km of 0.58 mM and a vmax of 1.6 pg/cellmin. The glucose diffusion coefficient in spheroids of 9L tumor cells was determined to be 1.5 × 10−6 cm2/s at 37°C. Using these parametric values, the glucose distribution in 9L multicell spheroids was calculated and related to the viable and necrotic zones.

Monolayer‐cultured 9L rat brain tumor cells grew optimally in culture media containing glucose concentrations greater than 0.07 mg/ml, but growth ceased at concentrations lower than this value. Assuming that this glucose concentration defines the proliferating fraction of cells in 9L multicell tumor spheroids, it is possible to simulate spheroid growth based on the intraspheroid glucose distribution derived by the author earlier. An excellent fit to experimental growth data was obtained by assigning the proliferating fraction a growth rate constant equal to 40% of that of monolayer‐cultured cells. This definition is in accord with our observation that the colony‐forming efficiency (CFE) of spheroid‐derived cells is 40% of the CFE of cells maintained in monolayer. This suggests that the role of glucose in 9L cell growth is similar in spheroids and in monolayer culture.