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/cell-min. The glucose diffusion coefficient in spheroids of 9L tumor cells was determined to be 1.5 x 10(-6) cm2/s at 37 degrees C. Using these parametric values, the glucose distribution in 9L multicell spheroids was calculated and related to the viable and necrotic zones.