Osteoprotegerin (OPG) is a soluble glycoprotein which inhibits osteoclastic formation and activity. Circulating OPG levels are elevated in uremia. The role of elevated circulating OPG levels in uremia remains unknown. Blood samples were obtained from 22 non-diabetic dialysis patients who underwent iliac bone biopsy examination. The serum OPG concentration was assayed by ELISA. The circulating OPG levels showed a negative correlation with the ratio of eroded surface/bone surface (ES/BS) in biopsied iliac bone samples among 15 of those with plasma intact PTH levels less than 300 pg/mL (P < 0.05, r(2) = 0.270). Patients with serum OPG levels less than 2.0 ng/mL showed significantly greater ES/BS values than those with levels > or =3.0 ng/mL, while the intact PTH levels were comparable among those groups. These tendencies disappeared when seven patients with plasma intact PTH levels more than 300 pg/mL were included into the analysis. In conclusion, circulating OPG levels showed a significant negative correlation with a bone resorption parameters in dialysis patients with mild secondary hyperparathyroidism. Circulating OPG might have a suppressive effect on osteoclastic bone resorption in dialysis patients.