Few studies have evaluated the occurrence of immediate adverse reactions in allergic patients after an ultra-rush regimen of different commercial allergen extracts for sublingual immunotherapy (SLIT) Methods: 679 patients took part in trials of specific ultra-rush SLIT for the treatment of IgE-mediated rhinitis and/or IgE-mediated asthma. 14 patients received two different sublingual allergen vaccines during two distinct SLIT sessions. On the whole, 699 SLIT sessions were performed. The build up ultrarush phase involved the administration every five minutes of increasing doses of either different allergen extracts. The cumulative allergen extract solution after half an hour was several times the dose administered at the start of subcutaneous immunotherapy (range 4.7-525 microg of major allergens). All patients tolerated the treatment very well. 122 (17.96%) had mild local symptoms (pruritus of the buccal cavity) that spontaneously disappeared with increasing dose. Two patients allergic to Parietaria had urticaria about three hours after the last sublingual Parietaria-extract intake. A subject allergic to Artemisia vulgaris pollen had urticaria and rhinitis two hours later than the last dose of vaccine. As reported in our previous study, no immediate severe adverse reactions were observed after that rapidly increasing doses of allergen extract were administered in a very short period to a large number of patients, showing the excellent safety profile of ultra-rush SLIT.