A 47 year old female with a history of hay fever and a family history of atopic eczema developed localized pruritic eczematous lesions over a three year period. The lesions became generalized within just three months. Episodes of recurrent erythroderma followed and became resistant towards any therapy. Many immediate and some delayed hypersensitivity reactions were diagnosed. In the peripheral blood, leukocytosis and hypereosinophilia were observed. In addition, levels of total IgE were highly increased in serum. Immunophenotyping of the peripheral blood T cells revealed evidence for a clonal expansion of highly activated CD4(+) T cells with reduced CD2 and CD5 surface expression. After a three-year course of severe disease, the diagnosis of a pleomorphic T cell lymphoma of the small-cell variant was established by histological examination and a polymerase-chain reaction technique to determine the rearrangements of the gamma chain of the T cell receptor. Moreover, analysis of cytokine gene expression suggested that the high IgE concentrations and eosinophil numbers observed in this patient were likely due to an increased IL-5 and IL-13 production by lymphoma T cells.