Increased eosinophil counts have been recognised to be linked to asthma severity and are a risk factor for asthma exacerbations. Therefore, decreasing eosinophil count by targeting the interleukin-5-mediated signalling pathway could help to reduce airway inflammation and improve asthma treatment control. In The Lancet Respiratory Medicine, Mario Castro and colleagues1 report data from two large, randomised, placebo-controlled trials, in which reslizumab, a neutralising monoclonal antibody for interleukin 5, was safe and effective in patients with severe eosinophilic asthma.