Ten ovalbumin (OVA)-specific T cell lines (TCLs) were established from peripheral blood mononuclear cells of 6 patients with hen egg allergy, and the antigen recognition of these TCLs was characterized. Two OVA epitopes were determined by use of 3 synthetic OVA peptides which have been known as murine T cell epitopes. Blocking of antigen-specific T cell proliferation by anti-HLA class II monoclonal antibodies suggest that all 3 HLA class II molecules could act as restriction elements for T cell recognition of OVA. This is the first demonstration of OVA epitopes recognized by T cells in patients with hen egg allergy, as far as we know.