OBJECTIVE: Recently, parathyroid hormone (PTH) was shown to support survival of progenitor cells in bone marrow. The release of progenitor cells occurs in physiologic and pathologic conditions and was shown to contribute to neovascularization in tumours and ischemic tissues. In the present study we sought to investigate prospectively the effect of primary hyperparathyroidism (PHPT) on mobilization of bone marrow derived progenitor cells. PATIENTS AND METHODS: In 22 patients with PHPT and 10 controls defined subpopulations (CD31⁺, c-kit⁺, CXCR-4⁺) of circulating bone marrow-derived progenitor cells (BMCs) were analyzed by flow cytometry. Cytokine serum levels (SCF, SDF-1, VEGF, EPO, and G-CSF) were assessed using ELISA. Levels of PTH and thyroid hormone as well as serum electrolytes, renal and liver parameters and blood count were analyzed. RESULTS: Our data show for the first time a significant increase of circulating BMCs and an upregulation of SDF-1 and VEGF serum levels in patients with PHPT. The number of circulating BMCs returned to control levels measured 16.7 ± 2.3 months after surgery. There was a positive correlation of PTH levels with the number of CD45⁺/CD34⁺/CD31⁺, CD45⁺/CD34⁺/c-kit⁺, and CD45⁺/CD34⁺/CXCR4⁺ cells. However, there was no correlation between cytokine serum concentrations (SDF-1, VEGF) and circulating BMCs. Serum levels of G-CSF, EPO and SCF known to mobilize BMCs were even decreased or remained unchanged, suggesting a direct effect of PTH on stem cell mobilization. CONCLUSION: Our data suggest a new function of PTH mobilizing BMCs into peripheral blood.