The first effort to develop an antibody against monobromo-tryosine was published in 1930, the most recent report in 2009. These prior researchers were able to generate a related antibody, against dibromo-tyrosine, but failed in their attempts to generate a reagent that reacts with monobromo-tyrosine. We utilized novel approaches to generate a unique antigen for immunizing mice, and these methods produced an antibody that reacts with monobromo-tryosine, although this antibody also reacts with other halogenated tyrosine residues. Eosinophils and neutrophils, two types of inflammatory cells, produce chemicals that cause halogenation of tyrosine residues. Analysis of sputum samples indentified a number of proteins that are more heavily halogenated in asthmatics than in healthy controls, and asthmatics with high eosinophil counts had higher levels of protein modifications than asthmatics with low eosinophil counts. Since many drugs for asthma target inflammatory processes, these results suggest that our antibody could be used to monitor (and maybe predict) drug responsiveness in asthmatics.