The paper reviews personal studies aimed at identifying clinical marke
rs of eosinophil inflammation in allergic diseases. Preliminary data o
n the use of how cytometry as a method to detect eosinophil activation
through phenotypic activation markers are reported. The concept of eo
sinophil releasability is introduced on the basis of in vitro eosinoph
il activation and mediator release by different stimuli. Data showing
an increase of serum levels of ECP mainly in subjects with sensitivity
to perennial allergens and related to histamine bronchial reactivity
are discussed in view of their practical impact in diagnosing and moni
toring of allergic diseases and asthma.