The data from high dilution experiments have caused a great deal of controversy in the past 20 years. The first results obtained by a manual method [1] were not reproduced by independent laboratories [2], although they were confirmed in a subsequent multicenter trial [3]. In 1994, our group published the first results analyzing basophil activation by flow cytometry after labelling with anti-IgE and anti-CD63. As this method produced promising results for allergy diagnosis, we also used it to examine basophil activation in the presence of high dilutions of histamine. Due to the availability of new reagents, we modified our first protocol. First, the anti-IgE was replaced by an anti-CD13 and then a new activation marker (CD203c). Due to the presence of a high percentage of contaminating monocytes, we added anti-CD14 and set up another three colour protocol. Since the results with allergy diagnosis demonstrated that IgE may also be considered as an activation marker, we set up a simplified two colour protocol based on basophil labelling with anti-IgE and anti-CD203c, the latter being basophil specific. We present here the results obtained by these four different flow cytometric protocols.