Osteoporosis, a condition in which bone mass is low, represents a major public health problem in developed societies. It may affect as many as 20 to 25 million people in the United States, and it is responsible for 1.3 million fractures each year, typically fractures of the spine, wrist, and hip. Osteoporosis exacts an enormous toll in morbidity and mortality, and its cost in the United States has been estimated at 7 to 10 billion dollars in 1986 alone. Predominantly, but not exclusively, osteoporosis is a disorder of women. The frequency of osteoporosis and osteoporosis-related fractures is expected to increase, because the most susceptible population-the elderly-is expanding.