The bcl-2 oncogene has been involved in the genesis of various B-cell neoplasms by means of encoding for p26, an apoptosis suppressor oncoprotein. The expression of p26 in lymphoproliferative disorders of large granular lymphocytes (LDLGL), a group of diseases whose mechanism leading to lymphocyte expansion is not yet clear, was not previously characterized. In order to further understand the biology of LDLGL, we compared the expression of p26 in CD8(+) lymphocytes of patients with CD3(+) LDLGL with that observed in normal individuals, patients with viral infection and patients with CD4(+) lymphoid neoplasms. We observed that upregulation of bcl-2 expression is not involved in the genesis of lymphocyte expansion in CD3(+) LDLGL. By contrast, when compared to normal peripheral blood counterparts, CD8(+, bright) lymphocytes of patients with LDLGL express low levels of p26 whereas CD8(+, dim) lymphocytes express normal or only slightly reduced levels of this oncoprotein. A similar pattern of expression of p26 was found in situations in which CD8(+) lymphocytes represent reactive activated cells.