This laboratory has carried out the first detailed studies of the active polymeric forms of phosphofructokinases over the concentration region of 1 to 1200 micrograms/ml. This includes the concentration range in which the enzymes exist in vivo and the concentration range in which their association-dissociation equilibria shift to yield various polymeric forms. Previously, active enzyme centrifugation experiments were limited to the concentration range below a few micrograms per ml. The present experiments were made possible by the recent development in this laboratory of a new technique called high concentration active enzyme centrifugation (Wei, G. J., and Deal, W. C., Jr. (1979) Biochemistry 18, 1129). We report here three new active polymeric forms of pig kidney phosphofructokinase which have been observed in high concentration active enzyme centrifugation experiments. These include: 1) a 9.8 S form (Mr = 2.6 X 10(5)); 2) a 25 S form (Mr = 1.01 X 10(6)); and 3) a 53 S form (too asymmetric to estimate Mr). In addition, a 5.4 S form is predicted from the Mr (8.8 X 10(4)) of the polypeptide chain obtained from sodium dodecyl sulfate gel electrophoresis; it is not known whether or not it is active. The 9.8 S value is the limiting sedimentation coefficient value observed in active enzyme centrifugation experiments. The 25 S form is indicated by a plateau in the 50 to 200 micrograms/ml region of the s versus c curve. The 53 S form is observed as a plateau in the 600 to 1000 micrograms/ml region of the s versus c curve.