We study semidilute and concentrated solutions of mononucleosomal DNA at three different NaCl concentrations by static and dynamic light scattering, viscosity, and electron cryomicroscopy. At low enough DNA concentrations the second virial coefficient behaves in the usual manner and can be interpreted by a charged rod model. It is possible to understand the concentration and scattering vector dependence of the scattering with the help of recent theoretical analyses of semidilute solutions of charged rods. Moreover, the mutual friction coefficient is in accord with the theory of hydrodynamic screening. At a certain critical concentration which increases with added salt, the intensity of the equilibrium static scattering increases several 100-fold, indicating the DNA aggregates. The dynamic scattering is in line with the static scattering; a very long decay time seems to be associated with the DNA aggregates. Freeze electron micrographs definitely bear out the existence of DNA globules which appear to form loose aggregates. Precautions have been taken to ensure there are no spurious contaminants to the best of our knowledge. Long-range attractive forces between polyions have been postulated recently within the framework of a semiquantitative theory; these ideas are tested by analyzing the ionic-strength dependence of the third virial coefficient and the onset of aggregation.