Cow red cells, under in vitro incubation conditions, exhibit a comparatively low glycolytic rate of 0.56 +/- 0.05 micromol/(ml cells.h), with a ratio of lactate formed to glucose consumed of 1.58. It has been found that this low glycolytic rate can be stimulated 50--60% above the basal level in the presence of a variety of purine and pyrimidine compounds including adenosine, inosine, adenine, hypoxanthine, xanthine, and uracil. In contrast, calf red cells, which have a much higher glycolytic rate, display no discernible response to these agents. In attempts to elucidate the mechanism by which this stimulation takes place, both glucose transport and glycolytic enzyme activities were determined in the presence of these stimulators. Glucose influx in cow red cells, measured using the glucose analog 3-O-methyl-glucose, exhibits both a low Km of 117 microM and a Vmax of 0.38 micromol/(ml cells.min), and is unaltered in the presence of adenosine. On the other hand, hexokinase, which in normal hemolysates of cow red cells has an activity of 0.49 +/- 0.03 micromol/(g Hb.min). was found to be stimulated to 0.73 micromol/(g Hb.min) in the presence of adenine. Both pyruvate kinase and phosphofructokinase were unaffected by this compound. These data suggest that certain purines and pyrimidine compounds may exert their stimulatory effect on hexokinase activity, resulting in an augmentation of cow red cell glycolysis.