Investigation of the synergism between absorbers (UVA) and antioxidants (A) for photostabilization of polydienes and polypropylene (PP) has revealed that synergism may be attributed to diffusion of A from the deeper-lying layers of polymer, protected from the action of light by UVA, towards surface layers where the photoreaction takes place. With PP, where additives are irregularly distributed in the amorphous phase, the mixture of the same stabilizers may lead to a synergism effect due to UVA quenching the excited electronic state of A, suppressing its photoinitiating effect. Also considered is the synergism attributed to an increase in solubility and a change in stabilizers' distribution pattern through introduction of low molecular weight stabilizing or non-stabilizing additives into polymers. See also AATA 18-797. -- AATA