There is a correlation between the clinical expression of various allergic disorders and an abnormal production of IgEs. A series of factors were recently described which are probably involved in this hyperproduction of IgEs: the IgE binding factors SFA and EFa, the glycosylation enhancing or inhibiting factors GEF and GIF and interleukin 4. It seems that there is also a correlation between the incidence of viral infections of the respiratory tract and an abnormal production of IgEs. Finally there are hereditary predispositions for the development of allergic diseases. It is interesting to try to group in an hypothetical scheme all the different factors which seem to act in conjunction to produce a shift to an IgE overproduction by atopic B lymphocytes.