We had been able to classify 70 cases of acute lymphoblastic leukemia (ALL) into different immunological subtypes based on surface marker analysis with the aid of a panel of monoclonal antibodies. The relative proportions of different ALL subclasses appears to be similar to those reported from Europe and the U.S.A. Our results also indicated that monoclonal antibodies OKT11, UCHT-2 and WT1 were very useful in defining pre-T or early T subtypes of ALL. The latter leukaemias lack most maturation-linked T-cell markers but share with the other T-ALL the characteristic of low density or undetectable insulin receptors.