This study describes the synthesis of polynorbornene colloidal particles able to release active molecules in response to pH change. Such functionalized polynorbornene latices with surface active molecules have been obtained by ring-opening metathesis copolymerization in a dichloromethane/ethanol medium in the presence of alpha-norbornenyl poly(ethylene oxide) macromonomer. Two different strategies of introduction of the active molecule-either at their periphery or at their core- have been contemplated. The particles have been characterized by both dynamic light scattering and transmission electron microscopy. Their size was found to range from 260 to 600 nm. The release of the active molecules was monitored by UV spectrometry. After 48 h in an appropriate HCl buffer (pH = 3) more than 80% of the initially linked active molecule was released. (C) 2004 Wiley Periodicals, Inc.