The aim of the project is to conduct a proof of concept study of a new and previously untested strategy to treat asthma. We have shown in animal experiments and in isolated human airways that a combination of three different drugs can fully protect the airways against asthmatic airway narrowing. The antagonists block three groups of mast cell signaling molecules: histamine, prostaglandins and leukotrienes. We have also shown in clinical trials in asthmatics that when two of these drugs (antihistamine and leukotriene antagonist) are combined, partial protection against allergen-induced airway narrowing is obtained. Our hypothesis is that the pretreatment that has been experimentally shown to be effective will also fully protect allergic asthmatics against the standardized asthma attack obtained during controlled exposure to allergens, so-called allergen provocation. In the trial, asthmatics will be pre-treated in a randomized order with placebo, or various combinations of the active substances montelukast (registered leukotriene antagonist), desloratadine (registered antihistamine), and ramatroban (prostaglandin antagonist that will be imported from Japan where it is used for hay fever). Ramatroban blocks the receptors for prostaglandins that are suspected to be involved in asthma. The project is testing a Swedish basic research discovery with the potential to create a new future low-cost alternative for tablet treatment of asthma.