The authors review the status of knowledge on absorption and kinetic of allergens administered on nasal mucosa. Intranasal administration is well known in pharmacology, and has been used for a long time for peptide drugs, mainly hormones. The immunological response to intranasally administered antigens have been studied in some experimental models: bovine Rnase, dextran, KLH, tetanus toxoid. These studies showed in atopic people a greater absorption of antigens by nasal mucosa compared to normal individuals, a difference that might be of importance in the pathogenesis of atopic diseases. The absorption rate of peptides through nasal mucosa has been studied biologically by PK-test with Rnase and peanut allergen, and a consistent passage of intact molecules has been observed. Using as tracer 125I-labelled human albumin, transport across the nasal mucosa has been demonstrated in 3/9 normal subjects, 1/9 patients with extrinsic asthma and 9/10 patients with atopic rhinitis. In experimental animals (rabbits) the passage of allergens through the nasal mucosa has been confirmed using 125I-labelled Parietaria allergens that showed a peak in the bloodstream 60 min after administration. It is concluded that peptide molecules such as allergens can be absorbed through the nasal mucosa and reach the bloodstream, and that in atopic patients nasal permeability is enhanced.