The microwave absorption characteristics of various forms of DNA in the frequency range between 0. 1 and 12 GHz are analyzed. The results are summarized as follows: the microwave absorption of aqueous solutions of long-chain DNA (tens of thousands of base-pairs in length) is not significantly different from the background absorption of the solvent; long-chain DNA that has been extensively sheared can exhibit substantially higher absorption per mass than the solvent; long-chain DNA that is nicked and subsequently broken into shorter fragments by the action of the endonuclease DNAse 1 will show a microwave absorption that rises with time during the action of the endonuclease. This strongly suggests a length dependence of the microwave absorption, and monodisperse aqueous solutions containing DNA molecules of well-defined length exhibit distinct absorption resonances. These resonances are surprisingly narrow.