By reflecting 10‐cm microwaves from the trails of ultra‐speed pellets, the ion (electron) density in the trails was found to be from 109to 1013electrons per cm of path length. Column diameters were from 1.0 to 7.5 cm and pellet velocities ranged from 1.48 to 2.67 km/sec. The ions appeared to come from thermal ionization behind the pellet shock waves and from oxidation reactions involving material ablated from the pellets.