A fascinating study in the January 2000 issue of the Journal of Allergy and Clinical Immunology suggests a powerful way to detect whether allergies are a problem. In this study, investigators measured the levels of nitrous oxygen (NO) gas in the breath of asthmatic children who had known dust mite allergies. These children were then moved to an environment without dust mites. The exhaled NO levels plummeted within 2 weeks, and remained low for 3 months. When the children returned to a normal environment, the levels went back up within 2 weeks. This test might turn out to be a great way to tell if it is really worth the cost to find a new home for the family kitty, move the family to a different region, or keep up with relentless dust-proofing.