To determine the utility of Ulex Europaeous Agglutinin I (UEA 1) as a marker for megakaryocytes, bone marrow from one hundred cases with various diseases studied using an immunoperoxidase method on the B5 fixed, decalcified and paraffin-embedded specimen. Our results indicated that large typical megakaryocytes and small megakaryocytes (micromegakaryocytes) were intensively stained by UEA 1 in diffuse, marginal, focal and hypo-granular patterns. Compared with factor VIII-related antigen, UEA 1 was more sensitive as a marker in identification of megakaryocytes. It provided an effective tool to observe the morphologic appearance of megakaryocytic lineage on B5 fixed, decalcified, paraffin-embedded specimen. The facility to identify the small atypical megakaryocytes as well as the different staining patterns would be helpful in the diagnosis of megakaryocytic disorders.