Thirty cases originally diagnosed as B-cell lymphomas, either LP immunocytoma, centrocytic (Cc), or centroblastic-centrocytic (Cb/Cc), containing follicular structures of an uncertain nature were critically reviewed using both morphological criteria and immunological techniques. In particular, they were tested by conventional antisera for detection of immunoglobulins in paraffin sections and also, in the 5 cases in which frozen material was available, by a panel of monoclonal antibodies. At the first histological evaluation the cases were divided into two groups. Group A consisted of 12 examples which showed homogeneous features and, because of the neoplastic nature of the follicular structures, could be classified as follicular centroblastic-centrocytic lymphomas with marked plasmacellular differentiation. Group B comprised 18 cases which at onset of disease revealed a mantle-fashion growth around reactive-appearing follicles formed by polytypic germinal centre cells. On closer examination, however, this group appeared heterogeneous: 13 cases displayed cytological and immunological findings consistent with the diagnosis of Cc and usually contained polytypic plasma cells; 5 cases were examples of LP immunocytoma consisting of monotypic elements only. Therefore, the so-called mantle-zone lymphoma does not appear to be an entity.