Purpose: Polyclonal IgG, IgA, and IgM immunoglobulins are often decreased in sera of patients with multiple myeloma (MM), whereas very few data are available on polyclonal IgE levels. We have determined IgE levels in a large series of MM patients at diagnosis and subjects with monoclonal gammopathy of undetermined significance (MGUS) and correlated IgE levels with survival and prognostic factors in MM. Experimental Design: IgE were determined with a commercially available ELISA kit in 201MM patients at diagnosis, 144 subjects with MGUS, and 77 age-matched controls. Results: IgE levels progressively decreased from controls to MGUS and from MGUS to MM (P = 0.001). MM patients with IgE levels of >11.5 IU/mL (median) had a better survival than patients with IgE of <11.5 IU/mL (P = 0.048). The difference was even more significant when MM patients were divided according to clinical cutoff values. Patients with elevated IgE levels (>100 IU/mL) had from 2 to 3 years longer survival than those with low (<10 IU/mL) or intermediate values (10-100 IU/mL; P < 0.01). IgE levels were positively and negatively correlated with hemoglobin (P = 0.006) and h2-microglobulin levels (P = 0.007), respectively. Univariate and multivariate analyses confirmed that high IgE levels are positive predictors of overall survival (P = 0.03 and 0.08, respectively) and strongly correlated with hemoglobin values. Polyclonal IgG, IgA, and IgM immunoglobulins are often decreased in sera of patients with multiple myeloma (MM) due to an increased catabolism and a decreased biosynthesis (1, 2). It is a matter of debate whether the extent of polyclonal IgG, IgA, and IgM hypo-g-globulinemia has a prognostic significance in MM at diagnosis or predicts development of active MM in monoclonal gammopathy of undetermined significance (MGUS). By contrast, very little is known on serum levels of polyclonal IgE (2 -4). In normal subjects, IgE synthesis is dependent on several factors, including the intrinsic properties and dose of antigen, the route of antigen delivery, the release of interleukin-4 from dendritic cells favoring the differentiation of naive Th 0 cells into Th 2 cells, the release of interleukin-4 and interleukin-13 from Th 2 cells, and the costimulatory interactions mediated by CD40/CD40 ligand between B and T cells (5 -9). As a result, total IgE levels are highly variable in general population, depending on many factors, such as age, gender, race, atopy, genetics, immune status, season of the year, tobacco smoke, and concomitant diseases (10 -15). Plotting the frequency distribution of IgE levels in a sample population on an arithmetic scale results in an overall distribution strongly skewed toward low values, with an isolated peak of very high IgE values. Replotting the same data on a logarithmic scale produces a Gaussian distribution (10, 11).Our interest on polyclonal IgE in MM originated from the immune monitoring of a group of patients treated at our institution with autologous idiotype vaccines and granulocyte macrophage colony-stim...