Exposure of aqueous solutions of the sodium salt of DNA to ionizing radiation at 77 K gives trapped electron-loss and electron-gain centers in the stacked bases that were well characterized by EPR spectroscopy. We find that when mitoxanthrone and AQ(4) are intercalated, the yields of the signals from the electron-gain centers are greatly reduced, being replaced by the EPR spectra of the intercalator radical anions. Fifty percent capture was observed for average intercalator separation of ca. 110 base pairs. At this concentration, the mean distance traveled by the ejected electrons prior to any type of capture is ca. 31 base pairs. These results are discussed in terms of their possible relevance to cellular DNA, with respect to both radiation damage and drug action. They are also compared with extensive work of others in this general area.