The allergen composition of a non-denatured extract of the storage mite Lepidoglyphus destructor was studied by a combination of hybridoma technology, sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) and a sandwich radio-allergosorbent test (four-step RAST). Using hybridoma technology, monoclonal antibodies (mAbs) were generated against the non denatured extract of the L. destructor. After screening by ELISA, mAb 42B6 was selected for further studies. This mAb specifically recognized an antigen of L. destructor of 39 kDa in SDS-PAGE. By a sandwich RAST, sera from 8 patients with known allergy to L. destructor were compared with control sera from 8 allergic patients. The results showed the presence of specific IgE against the 39-kDa protein in the sera of the test group, but not in the control group. There was also a good correlation observed between these data and the results obtained with the classical RAST. These results indicate that the newly identified antigen of 39 kDa is a major allergen of the storage mite Lepidoglyphus destructor.