Skin prick tests (SPT) with various celery, carrot and potato preparations (raw, cooked, cooking water of each vegetable and allergen extracts) as well as specific IgE determinations by RAST to celery mix, celeriac (or root celery), stick celery and heated celery extracts were performed in 70 patients with positive prick or intracutaneous tests to birch and/or mugwort pollens and celery (extract and/or raw). 94% of the patients showed positive prick tests to raw celeriac, 36% to cooked celeriac and 8/13 to cooking water. Celery-birch positive patients (n = 13) showed negative or low RASTs to heated celery extracts and to stick celery. By contrast, in the celery-mugwort sensitive patients (n = 6) the celery RASTs with heated celery extracts remained clearly positive and high RAST values to stick celery could be found. Celery-birch-mugwort-association (n = 22) favoured more positive results with relatively high values of RAST to celeriac. The results of homologous and heterologous RAST inhibition experiments with birch, mugwort, unheated and heated celery (100 degrees C) carried out in nine celery-RAST positive sera are also discussed.