Bone metabolism is characterized by continuous remodeling in which different cell lines, hormone systems and local mediators intervene. A useful method for the study of this process is evaluation of the physiopathological and clinical significance of substances which are involved in local turnover and at the same time are present in general circulation. These plasmatic markers are represented chiefly by bone-Gla-protein and alpha-HS-glycoprotein--peptides which belong to the more specific proteic component of the organic matrix in which reabsorption and neoformation take place, from the phosphatases to interleukin-1. Each one of these markers is described by analyzing the biochemical characteristics, the reciprocal correlations, and the potentials and limits in clinical practice. At present, none of these can guarantee formulation of a precise diagnosis of disease: they are, rather, biochemical indicators of the degree of bone turnover. The relevance of biochemical indicators becomes greater as the remodeling process increases, such as in Paget's disease. It lessens in conditions characterized by decreased cellularity such as osteoporosis. The study of these parameters during the course of therapeutic follow-up is extremely important.