The second harmonic generation in atactic-PMMA containing para-nitrosodimethylaniline (NDMA) and in PEO/PMMA blends containing 2, 6, 16 and 25 vol.% PEO doped with 4-anilino-4'-nitroazobenzene (Disperse Orange-3 dye, DO-3), is investigated. This work confirms an earlier finding that information on the mechanism governing the kinetic characteristics of the second harmonic signal decay in corona poled polymer systems can be obtained only through the simultaneous measurements of both the second harmonic signal and the surface potential, published by us. The results of the study concern the dependence of the second harmonic relaxation time on the temperature, the concentration of the optically non-linear molecules in the polymer matrix and the composition of the blends. The surface potential and second harmonic signal relaxation time, tau (e,) decrease more than 5 x 10(4) times when the amount of PEO in the blend is increased from 2 to 25%, while the rotational diffusion time always remains less than tau (e). Addition of hole transporting molecules into the optically non-linear composition based on 2 vol.% PEO speeds up the surface potential decay and strengthens the DO-3 rotational relaxation process. It is established that in the blends with low PEO concentration molecular alignment increases significantly around the temperature at which the cubic coefficient of thermal expansion starts to increase. (C) 2001 Elsevier Science Ltd. All rights reserved.