248 patients with non-Hodgkin lymphomas (NHL) were retrospectively analysed in an attempt to elucidate the risk factors, the prognostic importance and the therapeutic implications of blood involvement. Bone marrow involvement and large spleen were significantly correlated to leukaemic manifestations (P less than 0.0001 and P less than 0.0005, respectively); conversely no correlations were seen with bulky disease and symptoms. Among low-grade malignant lymphomas (LGML) centroblastic-centrocytic follicular and diffuse or diffuse and "CLL" subtypes were mostly associated with blood involvement (31% and 55%, respectively). Among high-grade malignant lymphomas (HGML) lymphoblastic type is more frequently associated with blood involvement (42%) than the other subtypes. Blood involvement was not clearly correlated with the prognosis either in LGML (median survival 39 and 36 months for leukaemic and non-leukaemic patients, respectively) or HGML (median survival 12 and 18 months, respectively), although a shorter survival of leukaemic than non-leukaemic lymphoblastic lymphoma was observed (median survival 8 months versus 14 months, respectively). The poorer response rate to therapy of leukaemic patients (median duration of CR22 and 5 months in LGML and HGML, respectively) as opposed to non-leukaemic patients (median duration of CR 29 and 23 months, respectively) led us to consider an alternative treatment in such patients.