The generation of high-energy relativistic electron beam pulses in the range of 50 MeV, 10,000 A, and 10's of ns is accompanied by very large background radiation that makes diagnostic measurements difficult. Although conventional fast-response radiation detectors can be used, they are expensive, noise sensitive, and bulky. Diagnostic techniques using radiation-resistant optical fiber transmissions, however, provide great flexibility and immunity to electrical noise for carrying out electron beam monitor and control functions, characterization, and propagation studies. The use of optical fibers enables the sensitive recording apparatus such as microchannel plate detectors or imaging tubes or streak cameras to be located in a benign environment. A beam propagation optical diagnostic system has been developed which uses optical fiber links to observe luminescence produced by the electron beam interaction with air or with fast scintillators, and to transmit the beam signature to a remote location. Various fibers were evaluated for this application, and their selection criteria are discussed. The diag-nostic system employing the fibers and the experimental results obtained for various beam propagation conditions using a Febetron Flash X-Ray source are also presented.