Antibodies are protein particles capable of specific antigen binding. Policlonal antibodies comprise of a group of antibodies that recognize different epitopes of the same antigen. Monoclonal antibodies recognize and bind to only one specific epitope. Both types of antibodies have their applica- tions in diagnostic techniques, however only monoclonal antibodies are used in flow cytometry. Conjuga- tion of monoclonal antibodies with fluorescent dyes enables the detection of antigens of different cell types. Contemporary flow cytometers can simultaneously detect more than ten different fluorescences, which gives the possibility of simultaneous assessment of many different antigens of the same cell.