1. Fructose 1,6-bisphosphatase from the white muscle tissue of the carp, Cyprinus carpio L. was purified. 2. The mol. wt of the enzyme was 145,000. Its subunit mol. wt was ca. 35,000. 3. The enzyme exhibited neutral pH optimum, activation by monovalent cations, and temperature-dependent allosteric AMP inhibition. 4. Carp muscle fructose 1,6-bisphosphatase was 10- to 30-fold more sensitive to AMP inhibition than the carp liver enzyme. 5. The carp muscle enzyme was less sensitive to AMP inhibition than the muscle enzyme from a homeothermic mammal. These results are interpreted as an example of temperature-adaptation of an enzyme regulatory property.