Several cell types, including mast cells, basophils, macrophages/monocytes, lymphocytes, platelets and eosinophils, may bind or contain IgE. To investigate the source of cell‐associated IgE and its relation to spontaneous IgE synthesis, peripheral blood mononuclear cells from allergic and non‐allergic donors were examined. Using a combination of different cell fractionation techniques and varying methods for extraction of cell‐associated IgE, data were obtained indicating that monocytes constitute a major source of cell‐associated IgE in human blood. The amount of cell‐associated IgE in peripheral blood mononuclear cells from allergic and non‐allergic donors varied more than 100‐fold but correlated closely to the level of serum IgE (r = 0.84, p < 0.001, n= 38). Spontaneous and mitogen‐induced in vitro syntheses of IgA, IgE and IgG were compared for allergic and non‐allergic donors. Only one donor with very high serum IgE demonstrated spontaneous or mitogen‐induced in vitro IgE synthesis despite synthesis of IgA and IgG.