Contiguous overlapping peptides (COPs) for the treatment of allergic patients by Specific Immunotherapy (SIT) are provided from the sequence of the major allergens of house dust mites Der p 1 and Der p 2. Such peptides while providing all potential T cell epitopes are devoid of the three dimensional structure of the original allergen, therefore reducing their ability to bind IgE. As a result increased amounts of COPs can be administered per injection, therefore reducing both the number of injections and the length of the immunotherapy treatment.