Tho characteristic energy loss spectra of five metals have been measured under clean, ultra-high vacuum conditions. Primary electron beams with energies of several hundred oV wore used and the 'reflected' secondary electrons were analysed by 127° electro-static analysers. The five metals studied were nickel, silver, tantalum, tungsten and platinum. High purity polycrystalline strips of each metal were thoroughly cleaned and mounted in a stainless steel vacuum chamber. Getter-ion and sorption pumps were used to produce UHV conditions, and tho targets were outgassed by resistive heating. The beam of primary electrons was usually incident at 45° to the target norma1 and those electrons scattered through 90° were focussed into the analyser entrance aperture. Tho final 127° analyser had ? resolution of less than O.9%. The characteristic energy losses observed in each spectrum have been correlated with the losses predicted by the theories of plasma oscillation, interband transition and subshell ionisation. In addition to a number of new losses, the present work has found most of the losses reported by previous authors. Evidence of contamination was seen in some spectra, even with the target in a vacuum of below 10-8 torr. The residual gases in the vacuum were analysed by a quadruple mass filter. It is suggested that the disagreements between previous workers have been due to the presence of contaminating layers.