It has been shown recently that the outer layers of vaccinia virions can be removed selectively under mild conditions to yield a preparation that consists entirely of "cores" (K. B. Easterbrook, Ultrastruct. Res. 14:484, 1966). Since these cores can be very easily ruptured and dissolved, they would seem to offer advantages over complete virions as starting material for the extraction of unbroken genomes. This note describes results obtained in an investigation into the morphology of DNA isolated from vaccinia viral cores by further detergent treatment
