Placzek proved that the collision density of neutrons coming from an energy point source and slowing down by isotropic elastic scattering in an infinite one-isotope nonabsorbing medium oscillates in a certain typical manner. It is proved in this paper that Placzek-type oscillations occur in one-isotope infinite media under the most general elastic scattering law and most general absorption law. In particular, the scattering need not be isotropic nor the absorption small or constant.