Haematopoietic cells in blood or bone marrow or both from 23 leukaemic and 10 control cats were characterized using cytochemical enzyme stains. The results changed the diagnosis based on clinical, haematological and histopathological findings in 4 (17%) leukaemias. Sudan black-B and chloroacetate esterase were granulocytic markers in both the control and leukaemic groups. Peroxidase activity was decreased in the granulocytes and monocytes of control animals but not in the blasts of leukaemic cats. Diffuse alpha naphthyl butyrate esterase staining marked monocytes in both control and leukaemic animals. Cytochemical staining was valuable for classification of feline leukaemias.