Zygophyllum fabago L. (Zygophyllaceae) can be found in the Middle East, in North Africa and in the arid zones of the Mediterranean region. It easily establishes itself in new regions, and is considered an invasive plant. They undergo ambophilous pollination, as there is a relationship between this type of pollination and its allergenic incidence. A combination of transmission electron microscopy with immunocytochemical methods was used to localize allergenic proteins during hydration and activation processes. Germination was induced in vitro for 1, 2, 4, 6, and 30 min. The activated proteins reacting with antibodies present in human sera from allergenic patients are found in the cytoplasm, intine, exine and exudates from the pollen grains. The activation time plays an important role on the labelling intensity. Labelling of allergenic proteins was abundant at 1 and 2 min of activation, and decreased at 4 and 6 min. The rapid activation and release of the allergenic proteins appears to be the main cause of allergenic activity of Z. fabago pollen grains.