The invention provides assay methods for the detection and quantitation of gastrin hormones, including total and free gastrin hormone in a sample. ELISA-type heterogeneous phase assays suitable for use with biological fluid samples such as blood, plasma or other bodily fluids of a mammal, particularly a human subject are provided. The method provides a precise assay for the amounts of free and total G17 and G34 in biological fluid samples, as well as the amounts of free and total Gly-extended G17, and Gly-extended G34. Also provided are methods of determining suitable treatment for patient suffering from a gastrin hormone-mediated disease or condition employing gastrin hormone immunoassays.