Acetone is a good marker of metabolic stress as it is the most volatile and rapidly equilibrated of the ketone bodies produced by human metabolism. If the body utilizes predominately fat to meet its energy requirements, blood and breath acetone concentrations will increase. Elevated concentrations of breath acetone can indicate a normal response to caloric imbalances in the diet, or a diseased state such as untreated diabetes. This paper describes a novel method of acetone detection that uses a gas-solid chemical reaction of acetone with a hydroxylamine hydrochloride (HA) to produce an easily detectable chemical species, HCl. Breath samples are passed through a reactor filled with solid HA and the amount of HCl gas released is measured by sensitive near infrared diode laser spectroscopy. The breath acetone instrument described is compact, low power and portable.