Binding of adriamycin-Fe3+ complex to phospholipids has been examined by phase partitioning in a hexane-water system. Formation of a stable ternary adriamycin-Fe3+-lipid complex with the negatively charged phospholipids cardiolipin and phosphatidylglycerol (both isolated from Escherichia coli) and synthetic dioleoyl glycerophosphoglycerol is demonstrated. Binding of adriamycin-Fe3+ complex to phospholipid bilayers was assessed by incubation of the complex with aqueous phospholipid dispersions prepared from synthetic dimyristoyl glycerophosphocholine, E. coli phosphatidylethanolamine or E. coli cardiolipin and from mixtures of these lipids. Binding of the complex to the phospholipids took place with an affinity for cardiolipin greater than phosphatidylethanolamine greater than phosphatidylcholine. The ternary adriamycin-Fe3+-ADP complex formed in the presence of 1 mM ADP (ADP in 25-fold molar excess to adriamycin) showed low affinity for binding to phospholipid.