Asthma is a multifactorial disease in which the hereditary component has been demonstrated by familial and identical twin studies. Allergy is important in the aetiology of asthma and is characterized by a hyperreaction to allergens triggering predominantly the immunoglobulines E. The levels of these antibodies are found to be elevated even in non allergic asthmatics. The majority of genetic research in this area is focused on either the genes of the specific immune response or that of the non allergic response. These are the genes of the class II MHC, and the APY gene on chromosome 11q respectively. The modern techniques of molecular genetics and in particular those of inverse genetics have recently contributed to a more comprehensive understanding of this disease.