Oriented fibers drawn from aqueous gels of calf-thymus DNA were maintained at constant relative humidites of 75 and 92% to yield canonical A-DNA and B-DNA structures, respectively. Raman spectra of the two forms of DNA were recorded over the spectral range 300–4000 cm−1. The authenticated DNA fibers were deuterated in hygrostatic cells containing D2O at appropriate relative humidities, and the corresponding spectra of deuterated DNAs were also obtained. The spectra reveal all of the Raman scattering frequencies and intensities characteristic of A- and B-DNA structures in both nondeuterated and deuterated froms, as well as the frequencies and intensities of adsorbed solvent molecules from which the hydration content of DNA fibers can be calculated. Numerous conformation-sensitive vibrational modes of DNA bases and phosphate groups have been identified throughout the 300–1700-cm−1 interval. Evidence has also been obtained for conformation sensitivity of deoxyribosyl CH stretching modes in the 2800–3000-cm−1 region. Raman lines of both the backbone and the bases are proposed as convenient indicators of A- and B-DNA structures. The results are extended to Z-DNA models investigated previously. Some implications of these findings for the determination of DNA or RNA structure from Raman spectra of nucleoproteins and viruses are considered.