It is widely accepted that single-mode (SM) fibre will be used in telecommunication networks and, in particular, in subscriber loops. In such mass applications, the cost and reliability of optical sources are important considerations which, together with recent developments in 1.3 μm edge-emitting LEDs, make the latter increasingly attractive compared with the lasers that traditionally been used in single-mode systems. Wavelength-division multiplexing (WDM) offers many advantages for such applications. Optical WDM devices for single-mode systems are currently available based on a variety of principles - e.g. interference filters, gratings, fused couplers, or a combination of these. The main purpose of this paper is to provide a quantitative comparison of the performance of these various types of WDM devices, when used with single-mode fibre and LED sources in applications such as the subscriber loop. System performance is measured in terms of insertion loss and received optical power levels, and crosstalk between WDM channels, as functions of temperature (-40 to +80°C); an important criterion for such applications. These measures are evaluated numerically, based on a mathematical analysis with parameters taken from published data to characterize the LEDs and WDM devices, and using measured values of the single-mode fibre characteristics. The results demonstrate the superiority of WDM devices using dielectric-thin-film, multilayer interference filters. Using these devices, the LED-based, single-mode-WDM system is shown to perform satisfactorily over the entire temperature range considered.