The intracellular levels of adenosine triphosphate and several glycolytic intermediates were determined in Saccharomyces cerevisiae in relation to the presence of the metabolically antagonistic enzymes phosphofructokinase and fructose-1,6-bisphosphatase. Phosphofructokinase is synthesized constitutively in cells grown in the presence of glucose and fructose-1,6-bisphosphatase derepression occurs upon the exhaustion of glucose from the growth medium. Transcriptional regulation of fructose-1,6-bisphosphatase was suggested based on experiments with wild type cells using 8-hydroxyquinoline, a known inhibitor of nuclear transcription, and with the S. cerevisiae mutant strain A364A (ts-136) blocked in the transport of nuclear RNA at non-permissive temperature. The level of phosphofructokinase was reduced more than 25-fold under conditions of high citrate accumulation in an aconitase-less, glutamate requiring mutant strain, MO-1-9B. There was a rapid decrease in the levels of adenosine triphosphate and fructose-1,6-bisphosphate at the end of log-phase of culture growth when both fructose-1,6-bisphosphatase and phosphofructokinase were present in the cells simultaneously. The changes in the levels of key glycolytic intermediates, but not the changes in adenosine triphosphate, during the simultaneous presence of these two enzymes, can be explained without involving any futile cycling.