The formation region effects in x-ray transition radiation have been experimentally investigated. The radiation was generated using 1–6 GeV electrons impinging on two multilayer targets with considerably different periods. The absolute yield of transition radiation was measured and the wide spectral peak in the range from 10 to 30 keV was observed. In the most part of the electron energy range the emission from the short-period radiator was expectedly suppressed, compared to the case of the long-period one. But for the electron energy of 1 GeV an opposite effect, though rather small, of the emission enhancement in the short-period radiator was observed. The conditions, under which this effect is much stronger, are derived and its possible practical value is outlined. The theory accounting for an arbitrary transversal shape of the electron beam and the finite size of the detector is developed. This theory describes rather well the experimental results.