Malignant lymphomas developing in tissue affected by a long-standing severe inflammatory process of nonautoimmune nature are presented. Two men and a woman aged 50, 58, and 73 years, were admitted after 22 to 30 year histories of pyothorax resulting from artificial pneumothorax for the treatment of pulmonary tuberculosis or tuberculous pleuritis. The diagnoses at admission were chronic pyothorax associated with a lung mass. Microscopically, tumors diffusely or locally proliferated with thickened pleura were present. A histologic examination showed that all the tumors were diffuse non-Hodgkin's lymphomas (NHL) of immunoblastic type with (one case) or without (two cases) plasmacytoid differentiation. Immunohistochemistry on paraffin sections revealed restricted expression of immunoglobulin light chains in one case showing plasmacytoid differentiation. A review of the literature showed that malignant lymphomas of this type have been reported exclusively from Japan but never from Western countries.