Severe equine asthma (SEA) is a common, chronic respiratory disease of horses characterized by hyperreactivity to hay dust which has many similarities to severe neutrophilic asthma in humans. A 2D immunoblot approach was used to identify quantitative differences in the recognition of the two-dimensional gel electrophoresis (2-DE) pattern between asthmatic and helthy horses´sera. Differentially regulated spots were cut from a 2-D gel and used for in-gel digestion followed by LC-MS to identify possible antigens.