Most peripheral T-cell lymphomas (PTCL) express the alphabeta T-cell receptor (TCR) whereas rare PTCL express the gammadelta TCR. Most if not all gammadelta PTCL are extranodal lymphomas and among them, hepatosplenic gammadelta PTCL constitute a distinct clinicopathological entity. Besides alphabeta and gammadelta PTCL, there is a recently recognized group of extranodal, mainly nasal tumours, which display, in most instances, phenotypic and genotypic features of Natural-Killer cell non-Hodgkin's lymphomas (NK-NHL). Cytotoxic cells, including NK cells and cytotoxic alphabeta and gammadelta T lymphocytes may induce lysis of the target by using granule-associated cytotoxic proteins such as the T-cell intracellular antigen-1 (TIA-1), perforin and granzyme B. Expression of TIA-1 can be detected in all cytotoxic cells whereas granzyme B and perforin expression can be detected in high levels only in activated cytotoxic cells. Recently, several studies showed that the expression of these cytotoxic proteins in tumour cells of PTCL and NK-NHL is associated with a) extranodal site of clinicopathological presentation b) NK or Tgammadelta-cell phenotype c) CD30 expression in cutaneous T-cell lymphoproliferations and d) anaplastic morphology in nodal PTCL. This latter finding contrasts with the data that only rare Hodgkin lymphomas (HL) express cytotoxic proteins in Hodgkin and Reed-Sternberg cells. Altogether the data of the literature indicate that most extranodal T and NK-NHL are activated cytotoxic lymphomas with the notable exception of hepatosplenic gammadelta PTCL which represent tumours of non-activated cytotoxic cells. On this basis, it is suggested that the expression of cytotoxic proteins may be useful for the identification and classification of extranodal T and NK-cell lymphomas and, to some extent, for the differential diagnosis between HL and CD30+ anaplastic large cell lymphomas. Cytotoxic lymphomas are preferentially localized in extranodal sites such as skin, lung, upper respiratory and gastrointestinal tracts, which are continuously exposed to various antigens. Since cytotoxic T and NK cells are regarded as first line of defense in these sites, and some cytotoxic tumours such as nasal lymphomas and enteropathy-type intestinal lymphomas are associated with EBV and gliadin, respectively, it is likely that chronic antigen exposure may play a role in the pathogenesis of cytotoxic lymphomas occurring in mucosa and/or skin. Besides chronic antigenic stimulation, chronic immunosuppression may also have pathogenetic significance in cytotoxic lymphomas in view of their increased incidence in immunocompromised patients.