The capacity of networks with multiuser receivers together with efficient usage of the resources, is analyzed in the uplink scenario of a single cell synchronous code division multiple access (CDMA) system. The capacity of the system is the maximum number of users per unit processing gain admissible in the system such that each user has its quality-of-service (QoS) requirement (expressed in terms of its desired signal-to-interference ratio) met. We characterize the capacity of a single cell for both the optimal linear receiver (MMSE receiver) and the matched filter receiver structures. This characterization of the capacity has a simple "effective bandwidth" interpretation. We also identify the "optimal" signature sequences and transmit powers to be allocated so that the users meet their QoS requirement.