Abstract. The interference of transition radiation coherently produced from a periodic stack of four polyimide foils of 7.2 btm thickness and a separation of 162 gm was investigated. This stack has been brought into the low emittance (3 rc nm rad) electron beam of the 855 MeV Mainz Microtron MAMI. Transition radiation was observed in the energy range from 2 to 15 keV with a LN2-cooled pin photodiode. A good energy resolution of 0.8keV and angular resolution of 0.15mrad was achieved simultaneously allowing for the first time to quantitatively study the interference pattern. Good agreement with theoretical calculations is found. Prospects to exploit transition radiation in the x-ray region from a low emittance electron beam as a high brilliant radiation source are discussed.