CD84 is a member of the CD2 subset of the immunoglobulin superfamily of cell surface receptors. Several members of this family are involved in the activation of T cells and NK cells. Although CD84 was originally cloned from a human B cell line cDNA library, very little is known regarding its biology on primary human leukocytes. We investigated the expression and biochemistry of CD84 on human B cells. CD84 was expressed on B cells in peripheral blood, spleen and cord blood. Two populations of splenic B cells could be resolved, CD84^lo and CD84^hi. CD84^hi B cells represented a subset of memory B cells as demonstrated by increased cell size, co‐expression of the memory B cell‐specific marker CD27, somatically mutated Ig variable region genes, and increased proliferation compared to CD84^lo B cells. CD84 became rapidly phosphorylated on tyrosine residues following ligation with a specific monoclonal antibody and recruited the cytoplasmic adaptor proteins SAP and EAT‐2. The ability of CD84 to undergo tyrosine phosphorylation and to recruit these SH2 domain‐containing proteins suggests it may function in the activation of B cells, particularly memory cells, and its signal transduction pathway may utilize SAP and/or EAT‐2. Thus, investigation of expression and function of CD84 and CD27 is likely to contribute to a greater understanding of the development and biology of memory B cells in normal and immunocompromised hosts.