Nitrocellulose membranes were activated by cyanogen bromide in order to improve their binding capacities. Crude extracts of a grass pollen, Dactylis glomerata, and a mite, Dermatophagoides farinae, were separated by isoelectric focusing in agarose and blotted by capillary transfer onto nitrocellulose or activated nitrocellulose. The Dermatophagoides farinae components were visualized by Coomassie Brilliant Blue, India ink or Aurodye staining. The Dactylis glomerata and Dermatophagoides farinae allergens were revealed by radioimmunodetection using sera from allergic patients. A great increase of allergen binding was observed visually and by radioactive counting on activated nitrocellulose as compared with untreated nitrocellulose. New allergens which were not detectable on nitrocellulose appeared on activated nitrocellulose.