Abstract. Although many governments have privatized their agricultural extension services, there is widespread agreement that the public sector still needs to play a role in the ''agricultural knowledge market'' in order to prevent market failure and other undesirable phenomena. However, appropriate mechanisms for intervention in the agricultural knowledge market are still in their infancy. This article discusses the case of the Nutrient Management Support Service (NMSS), a government-funded support service in The Netherlands designed to optimize the fit between the demand and supply of ''agricultural knowledge products'' that reduce nutrient emissions into the environment. The activities of the support service were four-fold: (1) distributing vouchers to farmers, (2) establishing mechanisms for quality control, (3) facilitating the articulation of end-users' needs, and (4) improving market transparency. We analyze the extent to which the NMSS has succeeded in supporting a demand-driven knowledge market for nutrient management issues. We question some of the conceptual and practical assumptions underlying this style of intervention. In addition, we argue that the notion of demand requires considerable refinement before it can be useful for guiding state involvement in demand-driven extension.Key words: Demand-driven agricultural extension, Knowledge markets, Nutrient management, Privatization, Public interest, State intervention, The Netherlands Laurens Klerkx holds a MSc in Tropical Land Use from Wageningen University. He is currently working on his PhD. His research focuses on how needs are articulated in demand-driven agricultural innovation processes and how newly emerging institutions such as knowledge brokers, knowledge networks, and innovation facilitators support this demand-driven agricultural innovation.Karin de Grip studied Tropical Agriculture (BSc) and, after working for 3 years in Indonesia in development cooperation, joined the MSc program in Management of Agri-ecological Knowledge and Social Change at Wageningen University. Her specific foci and interests include interactive knowledge development processes, learning processes, knowledge exchange and innovation networks, enforcement of knowledge markets, and demand-driven extension.Cees Leeuwis is professor of Communication and Innovation Studies at Wageningen University. He holds a MSc in Rural Sociology and a PhD in Communication and Innovation Studies. His research focuses on (a) the role of new interactive and cross-disciplinary approaches in bringing about coherent innovations, (b) the analysis of social learning and conflict management in networks, and (c) the way in which the privatization of research and extension institutions affects public sphere innovation processes.