237 elderly men and postmenopausal women, between the ages of 65 and 91 years old, with primary osteoporosis with up to 5 prevalent vertebral fractures caused by low BMD of the lumbar spine, were randomly assigned into 1 of 2 groups, a treatment and a placebo, to determine the effect a once a week administration of 56.6 microgram teriparatide had on bone mineral density and bone turnover markers 72 weeks after intervention. The results of the study indicated that percentage change in lumbar bone mineral density was significantly better in the teriparatide group when compared to the placebo treatment. One incident of vertebral fracture occurred in the teriparatide group compared to 16 in the placebo group. The percentage of treatment effect that could be explained by lumbar bone mineral density was 83%, as calculated by Freeman’s method.