One of the frequent causes of pollen allergy in our region (Serbia, Yugoslavia) is the pollen of poplar (Populus canadensis). The aim of this study was to form RAST for the determination of specific anti-Populus canadensis IgE antibodies. Affinity purified and radiolabelled (I-125) MoAb E1 was used for forming assay for the determination of specific IgE. By titration of extract of poplarPopulus canadensis we determined that the quantity of 0.65 mL extract is needed for coupling of lg BrCN activated paper discs. Coupling was performed in Na2CO3/NaHCO3 buffer pH 10, on 4°C for 48h. Using this newely formed RAST, specific forPopulus canadensis, we have deteminated anti-Populus canadensis IgE antibodies as well as cross reactivity between pollens ofPopulus canadensis andPopulus deltoides.