  We present mid-infrared spectra of the microquasar SS 433 obtained with the
Infrared Space Observatory (spectroscopic mode of ISOPHOT) and compare them to
the spectra of four Wolf-Rayet stars. The mid-infrared spectrum of SS 433 shows
mainly HI and HeI emission lines and is very similar to the spectrum of WR 147,
a WN8(h)+B0.5V binary with a colliding wind. The 2-12 micron continuum emission
corresponds to optically thin and partially optically thick free-free emission
from which we calculate a mass loss rate of 1.4-2.2x10^{-4} M_sun/yr if the
wind is homogeneous and a third of these values if it is clumped, which is
consistent with a strong WN stellar wind. We propose that this strong wind
outflows from a geometrically thick envelope of material surrounding the
compact object like a stellar atmosphere, imitating the Wolf-Rayet phenomenon.
