The preparation of polymer-drug complexes is one of the techniques used to obtain modified release formulations for use in different pharmaceutical forms. In this study, we prepared complexes with four commercially available latexes of different characteristics and two photoprotectors to determine the calorimetric, electrophoretic, and microphotographic characteristics of the complexes. The findings shed light on the interactions between the different polymers and drugs and on the differences between complexes as a result of differences in particle size. (C) 2008 Wiley Periodicals, Inc. Adv Polym Techn 27: 47-55, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20119