Materials and Methods Doxorubicin hydrochloride was provided by the Drug Synthesis and Chemistry Branch of the National Cancer Institute. Ferrous ammonium sulfate hexahydrate (99.999%) was obtained from Aldrich Chemical Co. All other chemicals were reagent grade or better and used as received. Glass-distilled water was used throughout the experiments. Ab-sorption spectra were measured in aqueous solution (pH 7.4) at room temperature in quartz cuvettes with a Perkin-Elmer recording spectrophotometer (Model 556). Anaerobic con-ditions were obtained by using previously published techniques (Burleigh et al., 1969) except that the solutions were purged alternating with argonand vaccum rather than with nitrogen and vacuum.