Reslizumab (Cinqair(®)) is a humanised monoclonal interleukin-5 (IL-5) antibody developed by Teva that has been approved in the USA for patients aged ≥18 years as add-on maintenance treatment for severe asthma with an eosinophilic phenotype. IL-5 stimulates the production, activation and maturation of eosinophils and is therefore thought to play a role in the development of bronchial hyper-responsiveness. This article summarizes the milestones in the development of reslizumab leading to this first approval for add-on maintenance treatment of severe asthma with an eosinophilic phenotype.