The present invention provides monoclonal antibodies (MAbs) selective for the N-termini and C-termini of the gastrin hormone forms, gastrin-17 (G17), glycine-extended gastrin-17 (G17-Gly), gastrin-34 (G34) and glycine-extended gastrin-34 (G34-Gly); and the hybridomas that produce these MAbs. Also provided are panels of MAbs useful for the detection and quantitation of gastrin-17 (G17), glycine-extended gastrin-17 (G17-Gly), gastrin-34 (G34) and glycine-extended gastrin-34 (G34-Gly). These assays are useful for monitoring a gastrin-mediated disease or condition, or for monitoring the progress of a course of therapy. The invention further provides solid phase assays including immunohistochemical (IHC) and immunofluorescence (IF) assays suitable for detection and visualization of gastrin species in solid samples, such as biopsy samples or tissue slices. Pharmaceutical compositions of the MAbs of the invention are also provided, along with methods of diagnosis, prevention and treatment of gastrin-mediated diseases or conditions. Methods of evaluating a gastrin hormone-blocking treatment are described. The course of a gastrin-mediated disease or condition may be monitored in a patient by means of assay methods provided.