Background The neurotrophins Nerve Growth Factor (NGF), Brain‐Derived Neurotrophic Factor (BDNF) and Neurotrophin (NT)‐3 are produced, stored and released by various immunological cells. The influence of NTs upon the function of these cells is described. Elevated plasma levels were found in inflammatory, autoimmune and allergic diseases with the highest levels in allergic asthma. A connection between bronchial hyper‐responsiveness and serum levels has been reported. Objective Little is known about the influence of treatment with inhaled corticosteroids (ICS) on serum NT levels and their influence on the asthmatic state. Methods Eighty‐seven volunteers were studied. Thirty‐eight were stable allergic asthmatics with constant ICS doses, 29 were asthmatics not receiving anti‐asthmatic treatment and 20 were age‐ and sex‐matched healthy controls. Demographic and lung function data were evaluated. NT serum levels were determined by ELISA. Results NGF and BDNF levels were significantly increased in untreated asthmatics compared to the control and the treated group, while NT‐3 demonstrated significantly higher levels in treated asthmatics compared to healthy controls. After stabilization of untreated subjects with ICS, the NT levels decreased significantly. Conclusions These results suggest that NTs participate in allergic inflammation and asthma. Effective treatment leads to a decrease of circulating neurotrophic factors.