The usefulness of SNR as a figure of merit to quantify the narrowband interference rejection capability of a DS receiver is examined. The interference considered is a peaked autoregressive Gaussian process. The probability of error and SNR estimates of a Kalman, a modified Kalman, and a nonlinear filter proposed in  are obtained by simulation. Based on this simulation study and the available theoretical error rate analysis of transversal filters, we can conclude that SNR is a useful measure if the processing gain, PG, of the DS system is moderately large. When the PG is small, such as 7, and if thermal noise is negligible compared to the signal, the SNR is not a reliable measure of performance.