The optical rotatory dispersion spectra of the following 16 viruses were measured: T2, T2(gt), T4, T6, T6(gt), λc, λ(K), λ(C), X174, T5, T7, B3, MS2, f2, R17 and α. T2 ghosts and T2, λ(C), λ(K), T7 and X174 DNA's and R17 RNA were also measured. The effect of high concentrations of lithium chloride salts at neutral pH on the DNA molecule in solution was also studied in relation to the packing of the DNA into the head of bacteriophages. The influence of the protein coat on the optical rotatory dispersion is shown to be small in the region above 250 mμ for DNA viruses of high nucleic acid content (∼50%), and for those viruses with nucleic acid content of around 25 to 30%; it is small above 280 mμ. The optical rotatory dispersion spectra of different types of viruses are qualitatively and quantitatively different. However, a difference spectrum of the nucleic acid inside and outside the virus shows qualitative similarities among all the DNA viruses tested. This indicates that the packing of the nucleic acid inside the virus has a common characteristic. Furthermore, the optical rotatory dispersion of the intact phage cannot be explained as the simple sum of the optical rotatory dispersion of the nucleic acid plus that of the protein coat. But the optical rotatory dispersion of osmotically shocked phage can be obtained by summing the optical rotatory dispersion of the DNA plus that of the ghost in solution. Equations are developed relating the different components of phage structure with the optical rotation spectra of the virus.