Classification of acute leukaemia by light and electron microscope cytochemistry

Blast cells in 33 cases of adult acute leukaemia were investigated for signs of myeloid differentiation by light (Sudan Black B) and electron (peroxidase activity) microscope cytochemistry. All cases which were strongly Sudan positive were also peroxidase positive and electron microscopy is of no further value in these cases. In 11 cases the blast cells were Sudan negative and in 8 cases they were weakly Sudan positive: the results of the electron microscopical analysis would have altered the classification in 9 of these 19 cases. It is concluded that ultrastructural demonstration of peroxidase activity in blast cells is of value in the classification of acute leukaemia in cases with blasts either negative or only weakly positive for Sudan.