Laser light scattering has been used to investigate the thermal pretransition of dipalmitoylglycerophosphocholine vesicles with variable radius as obtained by the mild sonication method. Intensity changes in 90 Β° scattered light are observed at the pretransition for larger vesicles and actually increase with increasing vesicle size, reaching a constant value. This constant value is in good agreement with the value calculated from the refractive index data. The intensity ratio of scattered light at temperatures of 30Β°C and 40Β°C (14o/13o) approaches unity at a radius of small single-bilayer vesicle. This result is interpreted as no pretransition for small vesicles in agreement with the calorimetric results. An expression of the particle scattering factor is also presented for multilayered shells composed of anisotropic elements. It is shown numerically, using this expression, that changes in the lipid layer thickness and the tdting angles at the pretransition have no effects on the scattering factor. Therefore it is concluded that the intensity changes in scattered light reflect the changes in the refractive index of the vesicle originating m the polar head groups.