Subcutaneous allergen-specific immunotherapy (SCIT) may lead to a significant reduction in asthma symptoms, medication, and airway hyperresponsiveness according to a meta-analysis of 75 trials published until 2001, which included a total of 3,506 subjects of whom 3,188 had asthma. The following allergens have been studied: house dust mites, pollen, animal dander, Cladosporium and natural rubber latex. A considerable heterogeneity of the effects of SCIT has been reported. This finding is basically confirmed in this review where the more recent SCIT trials since 2001 are also included, comprising further 1,917 patients. SCIT cannot be recommended as an alternative to asthma pharmacotherapy, which continues to be the mainstay of treatment for symptom control. SCIT can be indicated in intermittent or mild persistent allergic asthma with normal lung function (FEV 1 >= 70%) and proven IgE-related sensitization with corresponding clinical symptoms after contact with allergens that cannot otherwise be avoided, such as pollen and house dust mites. At present, clear beneficial effects in asthma have not been shown for sublingual immunotherapy (SLIT), and SLIT is not recommended for the treatment of asthma. The available data from SIT studies in asthma justify, however, further well-designed studies in intermittent or mild persistent asthma. A common outcome parameter for asthma studies, e.g., the combined symptom and medication score, is urgently needed.