Freshly obtained leukemic cells from 64 patients with acute myeloid leukemia were investigated. Intracellular protein and enzyme content (myeloperoxidase (MPO), acid esterase with alpha naphthyl acetate (ANAE) and alpha naphthyl butyrate (ANBE) and lactate dehydrogenase) were measured together with the cell diameter and compared with FAB-classification, cytochemical staining and clinical features. Mean values of MPO and acid esterase discriminate between the pure myeloid leukemias, although overlap between various subgroups is considerable. No correlation between cytochemical and quantitative enzyme determination was found. The logistic regression analysis revealed a dependency of the occurrence of complete remission on protein and ANBE (p less than 0.01) content. We concluded that quantitative enzyme determination is an easily measurable parameter of maturation and may have prognostic significance.