Skeletal abnormalities in 12 patients with primary hyperparathyroidism, five patients with pseudohypoparathyroidism, and three patients with hypoparathyroidism were studied to compare the diagnostic sensitivity of bone radiologic examination to that of radionuclide studies using 99mTc-Sn-pyrophosphate (99mTc-PPi) a skeletal-seeking radiopharmaceutical. The results were compared with bone mineral content as measrued by the Norland--Cameron densitometer. Kinetic data of the blood disappearance and plasma clearance of 99mTc-PPi were obtained and compared with data of control subjects without evidence of parathyroid disease. Bone imaging with 99mTc-PPi may be more sensitive than routine skeletal radiographs and bone mineral analysis for the evaluation of skeletal abnormalities in patients with parathyroid disfunction. The enhanced plasma clearance of the tracer observed in patients with primary hyperparathyroidism may reflect the direct effect of excessive parathyroid hormone on the renal handling of 99mTc-Sn-pyrophosphate.