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.