Periodic Coriolis star nystagmus was produced in normal and unilabyrinthectomized cats. The phase lags of the horizontal and the vertical components were measured and plotted against the angular frequency of the applied horizontal rotation. An empirical exponential function was fitted to the experimental values in order to smooth their distribution. Taking as a basis these curves, the value of Π/Δ, Π/Θ, Δ/Θ, ωn and ζ were estimated for the horizontal and the vertical semicircular canals. The value of the damping factor, ζ, shows that the system is overdamped. A comparison between the nystagmic responses to separate and to simultaneous stimulation of the horizntal and vertical canals suggests that an important utricular hydrodynamic coupling might exist.