By histomorphometry bone biopsy specimens were evaluated from 10 patients with severe primary hyperparathyroidism (PHPT). The data suggest that the mean trabecular width and trabecular bone volume were slightly, but not significantly increased. As indices of bone remodeling activity, both trabecular osteoid surface and trabecular resorption surface were significantly increased indeed, indicating high bone turn-over occurred in PHPT. The dynamic study showed that much more trabecular bone surface was covered either with single or double tetracycline labels in PHPT than in control. The overproduction of osteoid in the patients leads to the accumulation of osteoid on the trabecular surface. Moreover, the mean osteoid width seemed to be thicker in PHPT than in control, suggesting the co-existence of osteomalacia, which might be a possible explanation for eucalcemia usually seen in the majority. Part of chinese PHPT patients.