Immunohistochemical analysis of bone marrow trephine (BMT) biopsies with monoclonal antibodies for the analysis of hemopoietic disorders has been hindered by the fixation and decalcification regimens which mask or destroy tissue antigens. This study evaluated the effect of microwave oven treatment on the quality of immunostaining of fixed decalcified trephine biopsies. The aim was to establish whether this method of pre-treatment would enable additional antigens to be detected. Fifty-eight monoclonal and 4 polyclonal antibodies to hemopoietic antigens were assessed to compare no tissue pre-treatment, proteolytic (trypsin) enzyme digestion and microwave oven heating. The microwave heating of the sections was performed by placing them in a boiling solution of 0.01M tri-sodium citrate for a total of 10 mins. Following microwave heating 14 antibodies that previously showed no reactivity in BMT biopsies gave positive staining and 9 antibodies previously known to detect antigens in the absence of pre-treatment gave enhanced staining. Other antibodies showed no staining improvement with microwave heating and some failed to give a positive reaction by any of the pre-treatment methods. Antigen retrieval utilizing microwave oven heating can expose antigenic sites for antibody binding in bone marrow trephine sections. However not all antigens are retrieved and there is variation between epitopes on the one molecule and their ability to be exposed by microwave heating. Utilizing antigen retrieval methods, the range of antibodies applicable to BMT sections is greatly expanded enabling the immunophenotypic analysis of the majority of hemopoietic disorders.