An in vitro pilot study was performed to determine whether basophil cell-bound specific IgE was correlated to serum-specific IgE and to basophil cell sensitivity during immunotherapy with a well-documented treatment. The findings showed a clear dissociation between these three parameters, which is in contrast to the situation before hyposensitization and to our previous study in a comparable group of non-hyposensitized patients, where highly significant correlations were observed. Further investigations are in progress to clarify whether the dissociation is involved in the clinical improvement.