Immunophenotyping of leukemia cells is generally performed on cells in suspension. These suspensions are usually prepared from anticoagulated peripheral blood or bone marrow samples but when anticoagulation is suboptimal clotted samples may reach the laboratory. In this study cell suspensions were prepared from clotted blood and bone marrow samples of leukemia patients by lysis of the clots with streptokinase. The cell suspensions were then labeled with monoclonal or polyclonal antibodies and examined by flow cytometry or fluorescence microscopy. Enough cells could be isolated from small volumes of clotted blood or bone marrow aspirate to determine the immunophenotype of the cells. The morphology of the cells was well preserved and accurate identification of the cells was possible. The immunophenotypes determined on clotted samples from four patients with acute myeloblastic leukemia, five with acute lymphoblastic leukemia and two with chronic lymphocytic leukemia were identical to those established using EDTA anticoagulated samples of the same patients. When no unclotted samples are available this approach may avoid the necessity for a new sample and the concomitant delay in treatment of the patient.