During holographic recording in pure (Pb5Ge3O11) and doped [(Pb1–xBax)5Ge3O11] lead germanate crystals, the diffraction efficiency is transiently enhanced at the initial stage. The enhancement is studied as a function of writing-beam intensity and of dark delay time between two successive recording processes and with openor short-circuited crystal surfaces. Homogeneous pyroelectric fields that arise from heating of the crystals by cw illumination are revealed to be the main mechanism for diffraction efficiency enhancement. The combined effect of pyroelectric fields and charge compensation is analyzed and used for the explanation of the observed phenomena. © 1999 Optical Society of America.