The anthracycline antitumor antibiotics occupy a central position in the chemotherapeutic control of cancer. They remain, however, antibiotics of the last resort and thus exhibit toxicity both to the neoplasm and to the host organism. As part of the continuing effort to dissociate the molecular processes responsible for these two separate toxicities, attention has been drawn to the intrinsic redox capacity of their tetrahydronapthacenedione aglycone moiety, and to the possible expression of this redox activity against those biomolecules for which anthracyclines have a particular affinity (polynucleotides and membranes). This review is a synopsis of the present trends and thoughts concerning this relationship, written from the point of view of the intrinsic chemical competence of the anthracyclines and their metabolites. While our ignorance is profound--the precise molecular locus of the antitumor expression of the anthracyclines remains unknown--there is now evidence that the relationship of the anthracyclines to the DNA (possibly requiring enzymatic cooperation) and to the membranes, with neither event requiring redox chemistry, may comprise the core of the antitumor effects. The adventitious expression of the redox activity under either aerobic conditions (in which circumstances molecular oxygen is reduced) or anaerobic conditions (in which circumstances potentially reactive aglycone tautomers are obtained) is therefore thought to contribute more strongly to the host toxicity. Yet little remains proven, and the understanding of the intrinsic chemical competence can do little more than lightly define the boundaries within which are found these and numerous other working hypotheses.