This paper addresses the problem of bit detection for a chaos-based multiple-access system. In particular, one considers the differential chaos shift keying modulation. It is assumed that the transmission channels are frequency-selective. Moreover, the channel coefficients and the channel delays are unknown to the receiver. It is only assumed that vague estimates of the minimum and maximum channel delays are available for the user of interest. In this context, the detection is achieved using a training sequence from which an LMS detector is derived. The theoretical performance results are compared to those of the optimal detector for which all channel characteristics are known. Simulation results are given, which confirm the theoretical study.