Ectopic PTH secretion by tumor cells has been described as the cause of hypercalcemia associated with malignancy in the absence of osteolytic bone lesions. Although there have been case reports of elevated PTH and hypercalcemia in patients with rhabdomyosarcoma, to date ectopic PTH secretion by malignant cells has not been definitively shown. The possibility of PTH production by pleural-based metastatic nasopharyngeal rhabdomyosarcoma cells in a 62-yr-old Japanese male with hypercalcemia was investigated. The patient's serum PTH level was found to be elevated at 62.22 pmol/L, and pleural fluid PTH level was 47.28 pmol/L and PTHrP level was 3.7 pmol/L. RT-PCR of mRNA extracted from rhabdomyosarcoma cells in the pleural fluid was performed with the addition of PTH and PTHrP exonic primer sets yielded only a cDNA fragment of approx 150 bp consistent with the expected PTH fragment. Sequence analysis of a nested primer PCR fragment confirmed PTH mRNA sequence. We believe this patient to have had hypercalcemia secondary to ectopic PTH secretion, as we have identified the presence of PTH mRNA in tumor cells. We speculate that the overexpression of PTH in rhabdomyosarcoma cells results from molecular rearrangement of the PTH gene. The finding of a normal PTH DNA sequence of the PCR fragment suggests the likelihood of alterations in regulatory sequences.