Abstract: The present invention relates to immunologically cryptic peptides; methods for their identification in individuals and populations and their use in diagnosis and therapy of pathological conditions such as asthma and allergy, and their use in screening for therapeutic activity. Such cryptic peptides are identified by a method which includes the steps of: 1) exposing T cells with the peptide in a primary challenge; 2) measuring the reactivity of T cells with the peptide in the primary challenge of step 1); 3) exposing pre-challenged T cells with the peptide in a secondary challenge, wherein the pre-challenged T cells are obtainable by exposign the T cells to the protein; and measuring the reactivity of the pre-challenged T cells with the peptide in the secondary challenge of step 3), and the peptide is a cryptic peptide if T-cell reactivity is observable in the secondary challenge but not in the primary challenge.