Eosinophil leukocytes accumulate in high numbers in the lungs of asthmatic patients and are believed to be important contributors to the tissue damage and lung dysfunction seen in this disease. Eotaxin was originally discovered as a potent eosinophil chemoattractant present in bronchoalveolar lavage fluid of allergen-challenged, sensitized guinea pigs. Purification and sequencing of the protein revealed it to be a 73 amino acid CC chemokine. Mouse, rat, and human eotaxins have since been discovered, all signaling through a single receptor. CCR3. which is highly expressed on eosinophils, and also on basophils and a subpopulation of TH2-type T lymphocytes. Two other CC chemokine eotaxins. 'eotaxin T and 'eotaxin 3'. have recently been discovered which have similar activity, signaling via CCR3. The eotaxins are believed to be important in regulating eosinophil recruitment in the asthmatic lung and in allergic reactions in general. Thus, the eotaxin receptor CCR3 is a prime target for the development of anti-asthma, anti-allergy drugs.