A panel of commercially available monoclonal antibodies (MoAbs) including LN1, LN2, MB2, L26, Leu M1, UCHL1, MT1 and L60 was used to evaluate a diverse group of neoplastic processes in 256 Zenker's-fixed, decalcified, paraffin-embedded bone marrow biopsies using the ABC immunoperoxidase technique. LN2 and MB2 were useful in delineating the extent of B-cell lymphoproliferative processes and in identifying interstitial patterns of involvement. The combined application of LN2, MB2 and UCHL1 had utility in differentiating B-cell from T-cell lymphoproliferative processes; in no instance was reactivity with LN2 observed in T-cell processes. The combined application of these three MoAbs was also used in differentiating benign reactive lymphoid aggregates from focal malignant B-cell proliferations. LN2 exhibited positivity with the Reed-Sternberg cells (RSC) of Hodgkin's Disease (HD) and significantly aided in the identification of these cells. Staining of RSC with Leu M1 was inconsistent and was observed in only 50% of cases of HD. Use of the entire panel of MoAbs together with more recently available reagents such as Cathepsin G, MAC 387 and neutrophil elastase was essential in optimally evaluating a particular lesion; none of these MoAbs used singly reliably differentiated myeloid from lymphoid, hematopoietic from metastatic, or reactive from malignant processes.