At an opportune time for aging Americans concerned about osteoporosis, the parathyroid gland and parathyroid hormone (PTH) are coming back into the medical spotlight--after 65 years of neglect as mere balancers of the body's CA2+ books, as evidence accrues for their crucial role in building bone. The three authors affiliated with the Institute for Biological Sciences (Ottawa, Canada) discuss the anciently evolved gland's hormone and its receptors, PTH as a stimulator of bone growth, and the clinical use of PTH. Hopefully, it will not take another six decades to discover the precise mechanisms and further therapeutic applications of these rising stars of the hormone establishment. Annotation c. by Book News, Inc., Portland, Or.