This paper is the first to investigate photocatalysis using a cutting-edge and energy-efficient solid-state light source: Ultraviolet (UV) Light Emitting Diodes (LED's). UV LED's do not involve mercury vapor, can be driven with direct current (DC), and have a long lifetime of 100 000 hours. UV LED's with a peak wavelength of 375 rim were tested for perchloroethylene (PCE) photocatalytic oxidation over Degussa P-25 TiO2. At a UV light output of only 49 muW/cm(2). the designed reactor delivers a PCE conversion of up to 43%. If the UV LED price continues to drop, it is very likely that UV LED's will replace UV lamps as the favored light source in photocatalysis applications.