Peripheral T cell lymphoma developed in two patients several years after an initial clinical presentation of eosinophilia, pruritic skin rash, and vasculitis with lymphocytic infiltrates. Despite treatment with combination chemotherapy, the patients survived less than six months after the malignant lymphoma emerged. Immunologic characterization of tumor cells demonstrated features characteristic of peripheral T cell lymphoma. T lymphocytes from one patient had the uncommon phenotype of T3-negative, T4-positive, T8-negative. Extensive functional studies of this patient's lymphocytes revealed a poor proliferative response as well as an inability to help in immunoglobulin production, despite the preponderance of T4 lymphocytes. It is hypothesized that this syndrome is a consequence of the activity of products elaborated by neoplastic T cells.