The scdimeiit;ttioii cocflicieiit of c d f thyiiius a i d of T i I)NA w:is dctcriiiiiictl :il sc:vc~~il c,oiic:eiitratioiis tip to saturation i i i solrit.ioiis of each of the following d t s : JIgCL, AIgBr?, and RIgSSO4. Under certaiii coiiditioris, :t plot of the prodrict of the i ~h t ive viscosity and sedimentation coellic.ieiit agaiiist the delisit y of the solritioii has beeir f o i u i d to be h e a r and to extrapolate to zero at a density correspoiidiiig t o that of the solvated molecule. This behavior was realized iii MgSOI solutioiis, the zero intercept, oc:c:uriing at a density of 1.41 g/cc, corresponding to : L water activity of 0.89. The prefereiiti:rl solvatioii of DNA in IIgSO, soliitioiis calculated f o r this valiie is 10.5 moles nater,/mole of iiurleotide, iii good agreemelit with pitblished valiies of sdvatioii of IIN.4 at the siiiiie water activity iii univalent salt solutioiis. Siiice hicar plots were i i o t obtaiiied i i i IIgCI, and AlgB1.2 soliitions, buoyant, densities c~iirld not be determilied iii these c:ises. The iioiilinear behavior observed iii MgClp and JIgBrz soliitioiis may be due to a ch:tiigc i i i shape of the DNA molecule at the lower water activities reitched iii these solritioiis. The possibility of increased 11K.4-solute iiiteractioiis iii AIgUrZ a i d IIgC12 soliit ions is also considered as :tii esplaiintioii for the difference i i i t)ehavior between 1 I g W . ~ :tiid the two magiiesii:m halides.