We have collected literature data on Galactic masers with trigonometric parallaxes measured by means of VLBI .
We have obtained series of residual tangential , \Delta V _ { circ } , and radial , \Delta V _ { R } , velocities for 107 masers .
Based on these series , we have re-determined parameters of the Galactic spiral density wave using the method of spectral ( periodogram ) analysis .
The tangential and radial perturbation amplitudes are f _ { \theta } = 6.0 \pm 2.6 km s ^ { -1 } and f _ { R } = 7.2 \pm 2.2 km s ^ { -1 } , respectively ; the perturbation wavelengths are \lambda _ { \theta } = 3.2 \pm 0.5 kpc and \lambda _ { R } = 3.0 \pm 0.6 kpc for a four-armed spiral model , m = 4 .
The phase of the Sun \chi _ { \odot } in the spiral density wave is -79 ^ { \circ } \pm 14 ^ { \circ } and -199 ^ { \circ } \pm 16 ^ { \circ } from the residual tangential and radial velocities , respectively .
The most interesting result of this work is detecting a wave in vertical spatial velocities ( W ) versus distance R from the Galactic rotation axis .
From the spectral analysis , we have found the following characteristics of this wave : the perturbation wavelength is \lambda _ { W } = 3.4 \pm 0.7 kpc and the amplitude f _ { W } = 4.3 \pm 1.2 km s ^ { -1 } .