A crude extract of Parietaria judaica pollen was obtained by means of extraction, centrifugation and dialysis, and studied by means of quantitative immunoelectrophoresis. Crossed immunoelectrophoresis, using a high-titer purified rabbit antibody fraction, showed that the pollen extract contained at least 26 antigens of which 18 moved towards the anode, 6 moved towards the cathode and 1 moved both towards the anode and the cathode. The allergens in the extract were identified by means of crossed radio immunoelectrophoresis. Nine of the 26 antigens were able to bind specific human IgE to their corresponding immunoprecipitates, and 4 of these antigens can be classified as major allergens. The apparent molecular weights of 17 antigens were determined by a combination of size exclusion chromatography and immunochemical analysis. Ten antigens had Kav values corresponding to molecular weights in the range of 10-40 kilodaltons, 1 antigen possessed an apparent molecular weight of less than 10 kilodaltons, and six antigens had molecular weights above 40 kilodaltons. Most of the antigens, as analysed by column isoelectric focusing, had pI values between 4 and 7. Crossed line immunoelectrophoresis using an extract of Parietaria officinalis shows that the antigens of this extract exhibit a high degree of identity with those of P. judaica.