A long term study with bivalent live influenza vaccine was carried out in 18 subjects with no previous history of egg protein hypersensitivity. Experimental conditions included a nine-fold vaccination schedule with collection of serum and nasal fluid. The parameters studied were determination of serium and local antibody formation as well as the demonstration of specific IgE antibodies in serum and nasal fluid. Our major interest was directed towards the question of potential sensitization after repeated doses of non-purified oral vaccine. The close medical follow-up of the subjects revealed no clinical signs of atopic reaction. There were no complaints regarding adverse reactions usually following local application of live influenza vaccines. Determination of total serum IgE rederately elevated levels before, during und after the trial; one vaccinated subject showed high concentrations prior to vaccination with no significant change during the experiment. That individual was ultimately classified atopic with a pronounced hypersensitivity to egg protein. Nevertheless this person tolerated nine doses of vaccine without side reactions and showed no significant increase in total or specific IgE antibodies. Concentrations of IgE in nasal secretion of non-atopic subjects are less than 2U/ml, whereas they are frequently higher in allergic patients and in the presence of nasal IgE levels greater than 4 U/ml one would expect a specific reaction to challenge allergens. In our vaccinees nasal IgE values were consistently within normal range, at no time exceeding 2.6 U/ml, even the atopic subject did not exhibit higher levels in nasal fluid. A correlation between systemic and local IgE antibodies revealed no pathognostic relations; in addition to this, specific IgE-serum-antibodies as measured in the RAST against ovalbumin allergen did not show any correlation to vaccination. These data present good evidence for the innocuity of the vaccine with regard to its repeated application in man.