Antibodies for a variant of intact parathyroid hormone (PTH) or its fragments which have at position 17 the amino acid serine which is phosphorylated [p(17) PTH] and methods of producing the same. The invention further includes various immunoassay methods which use the described antibody alone or in combination with other antibodies to determine the circulating levels of p(17) intact PTH (1-84) or fragments thereof in biological fluids. Such antibodies and immunoassays can be used in conjunction with other antibodies to detect all biologically active forms of hPTH present in biological fluids.