The performance of asynchronous Gaussian minimum shift keying (GMSK) direct-sequence spread-spectrum multiple-access (DS/SSMA) systems is evaluated using Parsley's approach. Taking into consideration the interchip interference caused by the Gaussian lowpass filter. a closed-form expression for signal-to-noise (SNR) at the output of a coherent receiver is derived and then used for system analysis. A system optimisation or evaluation based oil output SNR is efficiently carried out, compared with Monte-Carlo simulation.