  A huge optical luminosity of the supercritical accretion disc and powerful
stellar wind in the high-mass X-ray binary SS433 make it difficult to reliably
estimate the mass ratio of the binary components from spectroscopic
observations. We analyze different indirect methods of the mass ratio estimate.
We show that with an account of the possible Roche lobe overflow by the optical
star, the analysis of X-ray eclipses in the standard and hard X-ray bands
suggests the estimate $q=M_\mathrm{x}/M_\mathrm{v}\gtrsim 0.3$. We argue that
the double-peak hydrogen Brackett lines in SS433 should form not in the
accretion disc but in a circumbinary envelope, suggesting a total mass of
$M_\mathrm{v}+M_\mathrm{x}\gtrsim 40 M_\odot$. The observed long-term stability
of the orbital period in SS433 $|\dot P_b/P_b|\le 1.793\times
10^{-14}$~s$^{-1}$ over $\sim 28$ year period is used to place an independent
constraint of $q\gtrsim 0.6$ in SS433, confirming its being a Galactic
microquasar hosting a superaccreting black hole.
