A differentiation block with accumulation of immature myeloid cells characterizes acute myelogenous leukemia (AML). However, native AML cells often show some morphological signs of differentiation that allow a classification into different subsets, and further differentiation may be induced by exposure to various soluble mediators, e.g., all trans-retinoic acid (ATRA) and several cytokines. Combination therapy with ATRA and chemotherapy should now be regarded as the standard treatment for the acute promyelocytic leukemia variant of AML. Several agents can induce leukemic cell differentiation for other AML subtypes, although these effects differ between patients. Differentiation may then be associated with induction of apoptosis, and differentiation-inducing therapy may therefore become useful in combination with intensive chemotherapy to increase the susceptibility of AML blasts to drug-induced apoptosis. However, it should be emphasized that differentiation and apoptosis can occur as separate events with different regulation in AML cells, and future studies in AML should therefore focus on: A) the identification of new agents with more predictable effects on differentiation and apoptosis; B) the use of clinical and laboratory parameters to define new subsets of AML patients in which differentiation/apoptosis induction has a predictable and beneficial effect, and C) further characterization of how AML blast sensitivity to drug-induced apoptosis is modulated by differentiation induction.