I. Introduction RECENTLY, the field of metabolic bone disease has received prominent recognition because of the increased public awareness of the prevalence and problems associated with osteoporosis. Because of the enormous disability and health care costs resulting from this disease, attempts have been made to try to identify individuals at risk or those who have established disease for either preventitive or therapeutic interventions. This has led to a search for markers of bone mineral metabolism which will either help understand the sequence of bone loss and bone remodeling or identify those persons at risk from osteoporosis. One of the approaches that has yielded useful information is the examination of the role of collagenous and noncollagenous bone proteins in bone mineral metabolism. This review will deal with some of the recently discovered collagenous and noncollagenous bone proteins, especially bone Gla protein [(BGP) osteocalcin], and their relevance to bone mineral metabolism. In addition, more established markers of bone remodeling will also be discussed. Growth, modeling, remodeling, and repair are all required for the development and maintenance of the bony skeleton. Growth involves an increase in mass, and modeling describes alterations in shape.