Many routing protocols for MANETs do not promote a balanced use of resources among the participating nodes, since they are designed to optimize other criteria, such as the number of hops in the message path. This behavior is undesired in open MANETs, where all users cooperate to maintain connectivity and expect the system to promote a fair distribution of load. This paper presents a fairness monitoring service that rates the effort of each individual node with regard to the other nodes in its neighborhood, measured as the relative number of messages the node is required to forward. We show that this information can be captured by a service that monitors the packets exchanged in the network. We illustrate the benefits of this service by showing how this information can be used to bias DSR, such that the load distribution is improved.