The autor summarizes the information about human leukocyte antigens. Expression of membrane markers is included in accordance with CD (Cluster of Differentiation) classification. The CD molecules are used ubiquitously in human medical research, immunodiagnosis and treatment and also CD profiles are intended to be used by biologists, pathologists and clinicians generally. Profiles nearly 400 known leukocyte cell surface molecules are summarized in CD system (CD1-CD350). Most CD molecules are integral membrane proteins that have one or more pass through the plasma cell membranes. Knowing which regions of a protein are intracellular or extracellular is important in the selection of peptides for immunization, for the expression of domains of the protein, and to understand the interaction of the protein with other proteins. CD markers are great targets for diagnostic and research of different types of diseases as a potential treatment for a variety of tumors.