Distributed Hash Tables (DHTs) provide a scalable mechanism for mapping identifiers to socket addresses. As each peer in the network can initiate lookup requests, a DHT has to process concurrently a potentially very large number of requests. In this paper, we look at congestion control for DHTs. Our goal is to control the flow of lookup requests that are routed in the overlay network. We first show that congestion control is essential for certain applications with high lookup rates. We then present two congestion control mechanisms for DHTs and compare their performances in different network conditions.