The relative concentration of the aldolase x fructose-bisphosphate and of the aldolase x dihydroxy-acetone-phosphate complexes is regulated, in the steady state, by the nature of the accompanying glycolytic enzymes. Particularly in the presence of triose phosphate isomerase, the aldolase x dihydroxyactone-phosphate complexes are largely prevalent. This situation is very likely to hold in rabbit muscle in vivo. Aldolase and gyceraldehyde-3-phosphate dehydrogenase slowly form a complex; however, no evidence has been found for the direct transfer of glyceraldehyde 3-phosphate between the two enzymes.