A mobile ad hoc network (MANET) is a infrastructure less network comprising of mobile nodes which dynamically form a network without the help of any centralized administration. Frequently changing network topology needs efficient dynamic routing protocols. We compare the performance of two on-demand routing protocols for mobile ad hoc networks dynamic source routing (DSR) and ad hoc on-demand distance vector routing (AODV). We demonstrate that even though DSR and AODV both are on-demand protocol, the differences in the protocol mechanics can lead to significant performance differentials. The performance differentials are analyzed using varying mobility.