Abstract
The theory of Bohr and Lindhard for electron capture and loss by heavy ions penetrating through solids has been modified. It is concluded that the difference in the average equilibrium charge of fast ions traversing solids and dilute gases is mainly due to Auger processes which occur after the ions leave the solid. The charge states inside solids are — in disagreement with the deductions of Bohr and Lindhard — not much larger than those in gases.