Enzyme Immunoassay (ELISA) for the one-step qualitative/quantitative determination of Helicobacter pylori Antigen (H Pylori Ag) in human stools. Stools from patients are used as a source of sample for the determination of HP antigen. Microplates are coated with a cocktail of affinity purified mouse monoclonal antibodies directed to the most specific Helicobacter pylori antigens. In the 1st incubation, the solid phase is treated with the sample, previously extracted from stools, and simultaneously with a mixture of monoclonal antibodies to Hp, conjugated with peroxidase (HRP). After washing out all the other components of the sample, in the 2nd incubation the bound enzyme specifically present on the solid phase generates an optical signal that is proportional to the amount of H. pylori antigens present in the sample.