The purpose of this study is to examine how and to what extent cultural heritage institutions (CHIs) are currently using social media to create a culture of participation around their digital collections and services. An environmental scan of New Zealand CHIs with a social media initiative was conducted and four cases with considerable activities, participatory communication and user-generated contents were investigated. Two of these case studies are reported in this paper. The two sites were chosen, firstly, on the basis of their having levels of participatory activity significant enough to merit in-depth analyses; and, second, on their ability to provide contrasting examples of different approaches and practices. The purpose of the comparison is to highlight the different nature and extent of participatory culture and user generated/contributed contents. While one of the sites belongs to a major national institution, the other represents a regional, community-level initiative. Further, while one site employs a self-hosted Web 2.0 platform, the other utilises a third-party platform. Finally, while one is aimed primarily at displaying and promoting images from an archival collection while enabling user commenting, the other actively seeks contributions to share and co-construct local history stories.