The phenotypic features of 44 cases of sporadic Burkitt's lymphoma (BL) were investigated by monoclonal antibodies (MoAbs). The majority of cases were positive for HLA-DR (97 per cent), CD19 (100 per cent), CD20 (92 per cent) and CD37 (83 per cent) pan-B markers, in accordance with the B-cell derivation of the tumour; the B-cell restricted markers CD21, CD22 and FMC7 reacted with 28 per cent, 66 per cent and 75 per cent of cases, respectively. Of the mantle zone B-cell specific MoAbs, CD1c was always negative, whereas CD23 and 2.7 were positive with one and two cases, respectively. CD39 was weakly reactive on two specimens, one of which was CD23+. The germinal centre specific MoAbs CD10 and CD77 (Burkitt's lymphoma antigen) displayed a heterogeneous pattern of reactivity and allowed to identify 4 subgroups: CD10+/CD77+ (44 per cent), CD10+/CD77- (15 per cent), CD10-/CD77+ (36 per cent) and CD10-/CD77- (5 per cent). Of 15 cases tested for the expression of CD11a and CD18 lymphocyte-function-associated (LFA-1) antigens and their ligand ICAM-1 (CD54), seven were positive and six negative for the three markers, while the other two cases expressed alternatively the two molecules. Analysis of the putative normal BL cell counterpart, identified with the CD77 marker in normal lymphoid tissues, showed that all CD77+ B-cells were constitutively CD11a+/CD18+, suggesting that BLs are likely to arise from a LFA-1 positive B-cell and may down-regulate these molecules during neoplastic transformation.