We have made a comprehensive study of charge-changing cross sections in N2 of Pb and Xe ions at velocities near 4 X 10 cm/sec. We determine the velocity, ionization state, and Z dependence of the capture and ionization cross sections and make an extensive comparison with theory.Capture or loss of an electron by a fast very heavy complex ion colliding with an atom is one of the more refractory problems in atomic collisions. " For very heavy ions at velocities «10 cm/sec only a small amount of experimental information is available, Also, there is a general perception that theoretical models used for lighter and simpler ions may be inadequate. 2 In this Communication we present the first comprehensive study of charge-changing collisions of very heavy ions at velocities above 10 cm/sec.From experimental measurements of Pb (Z =82) and Xe (Z =54) ions in N~at velocities (relative to the speed of light) of p=v/c =0.134 and p=0.099, and Xe at p =0.072 we extract a total of 178 cross sections. We determine the velocity, ion charge, and nuclear charge dependence of these cross sections.