A report that a severe IL‐18/IL‐18BP imbalance results in Th1 lymphocyte and macrophage activation in patients with secondary haemophagocytic syndrome 25 may support the view that an IL‐18/IL‐18BP imbalance decides the role of IL‐18 in the pathogenesis of asthma. The gene discussed is IL18BP; the disease is hemophagocytic syndrome.