The invention provides a breath testing device which visually indicates the presence of ammonia in a patient's breath, in particular ammonia from helicobacter pylori urease infection. The breath testing device comprises a visual indicating agent which changes color in response to ammonia odors, such as 4,4'-bis(dimethylamino)-benzhydrol (Michler's hydrol or BDMB), pararosaniline base and alpha-naphtholbenzein. The indicating agent is applied to a substrate which is then inserted into a tube or straw, which can be attached to the inlet of a breath collection balloon. When the patient blows into the tube or straw, the indicating agent will change color if it detects levels of ammonia which are consistent with helicobacter pylori urease infection.