Space-time coding and multiuser detection are two widely used techniques that are known to substantially increase CDMA system capacity by using multiple transmit antennas and interference cancellation respectively. In this paper, we consider a space-time coded multiuser system based on real orthogonal designs. For this system, we study the performance of the minimum conditional probability of error (MCPOE) algorithm. The decision variable for MCPOE is the conditional probability of error, that is minimized to get the estimates of a set of filter coefficients. The filter coefficients are then used for symbol detection at the receiver. We find that the MCPOE algorithm scores over other adaptive multiuser detectors available in the literature, both in terms of convergence as well as bit error rate (BER) performance. © 2005 IEEE.