The hypothesis that certain nonparathyroid tumors associated with hypercalcemia contain a parathyroid hormone-like substance was examined experimentally. Biologic assays of extracts of the tumors in parathyroidectomized rats were negative or equivocal; factors involved in interpretation of the assays are discussed. Earlier published estimates of parathyroid hormone-like material in tumors, obtained by immunoassay of urea extracts of the tumors by a method utilizing direct complement fixation, were found to be too high because of a nonspecific reaction of the urea extracts. New evidence supporting the presence of parathyroid hormone-like material in hypercalcemic tumors was provided by data showing that HCl extracts of the tumors, like HCl extracts of parathyroid glands, specifically inhibit the direct complement fixation by purified bovine parathyroid hormone and anti-bovine parathyroid hormone. Factors that restrict the inhibition reaction to qualitative identification of parathyroid hormone-like substances are discussed.

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Contribution No. 372 of the Graduate Department of Biochemistry, Brandeis University, Waltham, Mass.

This investigation was supported in part by research grants from the National Institute of Arthritis and Metabolic Diseases (A-1787), USPHS, and the American Cancer Society (E-222).

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