On the character of SS 433 spectral variablity with the 6-day period (June-August 1981).

New spectral data (≡280 spectra) for the object SS433 obtained during 35 nights in the summer of 1981 with the 1000-channel spectrophotometer of the 6-meter telescope within the range λλ5300 - 7900 Å with a resolution of ≡4 Å are analysed. The behaviour of hydrogen and helium relativistic line profiles with time is studied and the following parameters for them are determined: equivalent widths W_λ, central intensities R_c, halfwidths Δλ(1/2) and radial velocities z. A detailed study has been given to the radial velocity variations in the main components of relativistic hydrogen lines Hα and Hβ with a 6-day (nutation) period.