The invention provides methods and materials related to the diagnosis of eosinophil degranulating conditions. Specifically, the invention provides methods and materials that involve visual types of analysis (e.g., microscopic analysis) that are used to determine the presence or absence of a horseshoe-shaped eosinophil granule structure within a mucus sample collected from a mammal. The presence of a horseshoe-shaped eosinophil granule structure within a patient's mucus indicates that the patient has an eosinophil degranulating condition. In addition, the invention provides methods and materials that involve immunological types of analysis (e.g., immunoassays) that are used to determine if a patient's mucus contains a tissue-damaging amount of eosinophil granule content that is outside the eosinophil granule and within the mucus. Like the presence of a horseshoe-shaped eosinophil granule structure, the presence of a tissue-damaging amount of eosinophil granule content outside the eosinophil granule and within the mucus indicates that the patient has an eosinophil degranulating condition. Further, the invention provides diagnostic kits that can be used to determine whether or not a patient has an eosinophil degranulating condition.