AbstractBy utilizing a novel approach to microwave spectrometry, we have measured the absolute absorption spectrum of plasmid DNA (pUC8.c2), in buffered aqueous solution, from 5 to 20 GHz. Our technique does not suffer from the same experimental difficulties that plague other methods. We observe no absorption resonances in this frequency range, but we do see broadband differences, between DNA and pure buffer, that are attributable to changes in the ionic conductivity of the solutions. These results constitute the first verification, by a totally different technique, of the absence of resonances in the microwave absorption spectrum of DNA, and the first data obtained by any technique in the 10–20‐GHz band. © 1993 John Wiley & Sons, Inc.