In amplified wavelength-division-multiplexed (WDM) networks, the performance of a low-frequency (<100 kHz) pilot-tone-based monitoring technique could be deteriorated by the slow dynamic properties of erbium-doped fiber amplifiers (EDFAs). We develop a simple model to describe this effect and estimate the maximum size of WDM network that the pilot-tone-based monitoring technique could support. The result shows that 100-kHz pilot tones could be used for the cost-effective monitoring of metro optical networks (32 channels, 320-km transmission). (C) 2008 Society of Photo-Optical Instrumentation Engineers.