Measurement of serum parathyroid hormone (PTH) concentrations is complicated by the fact that there are several fragments of the hormone in the circulating as a result of the metabolism of PTH. The best way to study the secretory activity of the parathyroid glands directly may be to measure the biologically active intact PTH molecule. Recently, it has become possible to overcome these limitations by application of the two-site immunoradiometric assay (IRMA) to the measurement of intact PTH. The two-site immunometric technique has been applied to the two-site immunochemiluminescent assay (ICMA) for the measurement of circulating intact PTH. To evaluate the utility of measurements of serum intact PTH by two-site ICMA in hemodialysis patients, two-site ICMA and IRMA were compared in 104 hemodialysis patients. We found a good correlation (r = 0.93) between values obtained by ICMA and by IRMA. Although serum intact PTH by ICMA was significantly suppressed by rising plasma ionized calcium after a session of hemodialysis in 29 patients, mid-region PTH did not show a significant change. This result suggests the intact PTH assay is more suitable for the earlier detection of secondary hyperparathyroidism than the mid-region assay and may be useful for precise assessment of clinical status and response to therapeutic intervention designed to correct the progressive bone disease in hemodialysis patients. We conclude that two-site ICMA for serum intact PTH which could be measured without radioisotopes nor scintillation counter is as useful as IRMA in hemodialysis patients.