The interaction of three second-generation anthracycline derivatives with polynucleotides, supercoiled DNA, and calf thymus nucleosomes has been studied by terbium fluorescence measurements and agarose gel electrophoresis. It was shown that, as expected, N-trifluoroacetyladriamycin-14-valerate had little detectable effect on the fluorescence of this guanine-specific probe except for polydisperse calf thymus linear DNA fragments. The soluble analogue, N-trifluoroacetyladriamycin-14-O-hemiadipate, did show marked effects on terbium fluorescence with all nucleic acids and nucleosomes, but the effects were generally not as striking as were those observed with the epimer, 4'-epi-Adriamycin, which tended to produce a similar effect to its parent drug, Adriamycin, showing that a marked change in the hexose ring did not appreciably affect the interaction of the drug with DNA. Changes in the electrophoretic mobility of supercoiled pBR322 DNA were observed only at very high drug concentrations, much higher than those required with Adriamycin or actinomycin D. The effect was a smearing of the form I DNA and the production of some circular relaxed form II DNA. The drugs produced the effect in the following order: Adriamycin greater than N-trifluoroacetyladriamycin-14-O-hemiadipate greater than or equal to epi-Adriamycin. N-Trifluoroacetyladriamycin-14-valerate had little effect, even at very high drug concentrations (1:2, drug:DNA ratios).