The paper examines in detail the frequency-domain method of analysing signals from laser Doppler systems, and theoretical relationships are formulated to predict statistical characteristics of frequency spectra obtained by this method. It is shown that, for the measurement of statistically stationary turbulent flow, both r.m.s., level and integral time scale significantly affect the spectrum chracteristics, and both these parameters can be measured by the frequency-domain method. It is also shown that the laser Doppler method can conveniently be used for the measurement of turbulence microscales. The theoretical results established in the paper are supported both by analogue simulation experiments and by measurements in a turbulent fluid flow.