Nine cases of lymphoblastic lymphoma and eight cases of small, noncleaved undifferentiated non-Burkitt's lymphoma were studied. All cases were stained with monoclonal antibodies, directed to the leukocyte common antigen (LCA), B- and T-cell markers as well as Calla. Small noncleaved, undifferentiated non-Burkitt's lymphomas were LCA positive and expressed one or more B-cell markers. Three cases of lymphoblastic lymphoma were LCA positive and showed reactivity with antibodies OKT4, OKT6 and OKT8. The six remaining cases of lymphoblastic lymphoma were LCA negative, except for only one case that was weakly LCA positive using more sensitive detection methods. Two of the LCA negative cases expressed Calla, and four cases did not show any reactivity with the monoclonal antibodies used. In all LCA negative cases, small residual non-neoplastic nodules representing remnants of lymphoid follicles, could be detected. Since five out of nine cases of lymphoblastic lymphoma were LCA negative, lack of staining for LCA does not preclude the diagnosis of lymphoma.