We review recent experimental work devoted to the characterization of the spectral profile and linewidth of two types of XUV lasers seeded by high-order harmonic radiation. The spectral properties were deduced from the measurement of the temporal coherence of the XUV laser pulse, using a variable pathlength interferometer. In this paper an optical-field ionization XUV laser developed at LOA laboratory (France), emitting at 32 nm, and a grazing incidence, and a transient XUV laser developed at Colorado State University (US), emitting at 18.9-nm, both operated in the injection-seeded mode, were investigated. We show that in both cases the measured temporal coherence length is slightly larger than when the lasers are operated in the amplified spontaneous emission (ASE) mode. The corresponding bandwidth is observed to be larger for the transient pumping system, which should more easily scale to sub-picosecond pulse durations.