A specimen introduction/reaction system is described for a transmission electron microscope modified for UHV operation. The dry-pumped and UHV-compatible reaction chamber can be used for subjecting microscope specimens to RF-plasma treatments. The plasma oxidation and reduction of an in-situ-deposited particulate palladium film supported on amorphous alumina is described. A significant degree of redispersion is caused by this low-temperature process. © 1987.