76 adult acute nonlymphocytic leukaemias (ANLL) were characterized by cytochemical markers and placed in a coordinate system. The position of each ANLL was determined on the basis of the peroxidase and nonspecific esterase reactivity of the blast cells. This classification numerically identifies the maturation tendency and heterogeneity of individual ANLL cases according to its position in the coordinate system. 49 ANLL patients were treated with TAD protocol and the response rate seemed to be in a conspicous correlation with the position of the individual ANLL cases in the modified arrangement. Cases exhibiting a strong peroxidase maturation, i.e. the cytochemical maturation index being 80% or more had a considerable higher complete remission rate and longer duration of remission than those with low (less than 80%) maturation index. Age profoundly influenced even this figure.