Although user involvement is frequently practiced in companies, the research findings regarding its benefits for innovation are contradictory. This article experimentally assesses the contributions made by users in comparison with professional service developers and examines how the implementation of user involvement affects the outcome. During periods of 12 days, three different groups were assigned the task of generating ideas for end user telecom services. One group consisted of professional de signers, whereas the other two consisted of ordinary users. The users in one of the groups coped with idea creation by themselves, whereas the other group consulted a service design expert at two controlled meetings who provided feedback regarding technical  feasibility. Involving users makes the ideas more original, holding a higher perceived user value, but the users’ideas are less producible on aver-age. The outcome was also affected by how user involvement was implemented. Scholarly and managerial implications conclude the article.