Two monoclonal antibodies (mAbs), XB6 and YD3, which recognise ovine immunoglobulin E (IgE) were produced. Mast cells isolated from ovine intestinal mucosa were used as a source of IgE to immunize mice. Culture supernatants of hybridomas were screened by immunoassays on small-intestine tissue sections, isolated mucosal cells, and dot blots of lysed mast cell homogenate. Two mAbs were chosen for their specific binding to mast cells. Antigen bound by these mAbs was purified by immunoaffinity chromatography using XB6 mAb, and this produced two bands consistent with IgE heavy chain (86,000 Daltons) and immunoglobulin light chain (28,000 Daltons) when run under reducing conditions on SDS-PAGE gels. Purified IgE was shown on dot blots to react weakly with mAb to chimeric ovine IgE and strongly to polyclonal anti-sheep antibodies. The two mAbs induced an immediate hypersensitivity-like reaction when injected into the skin of sheep. The mAbs bound to mast cells and other mononuclear cells, presumably IgE-secreting B-cells in mesenteric lymph node sections. These mAbs proved useful for detecting IgE-bearing cells in various ovine tissues, for purifying mast cells from cell isolates by panning and immunomagnetic bead separation, for purifying serum IgE using immunoaffinity chromatography and for detecting IgE in an ELISA. Competitive binding assays showed that the two mAbs bind to different epitopes on IgE. These mAbs will be useful in research applications and in diagnostic assays.