A survey of the existing data on the interactions of glycolytic enzymes with the cellular structure in mammalian tissues has substantiated the occurrence of an extensive degree of such associations in all tissues and during all stages of development. Furthermore, a considerable specificity was evident between the individual multiple forms of the enzymes in relation to these associations. In reviewing these data, a model has been developed which proposes that the glycolytic sequence is best described as consisting of a number of segments in vivo, each segment formed by a cluster of isozymes, many of which can interact with the actin containing filaments of the cytomatrix. The novel features of this segmentation and compartmentation have been described, and evidence has been provided that these phenomena collectively play a key role in meeting the different types of energy requirement in the cytoplasm of divergent cell types, with the wide selection of isozymes in this system offering the potential for increased flexibility and control in this important area of metabolism.