  We present VLT/FORS2 time-series spectroscopy of the Wolf-Rayet star #41 in
the Sculptor group galaxy NGC 300. We confirm a physical association with NGC
300 X-1, since radial velocity variations of the HeII 4686 line indicate an
orbital period of 32.3 +/- 0.2 hr which agrees at the 2 sigma level with the
X-ray period from Carpano et al. We measure a radial velocity semi-amplitude of
267 +/- 8 km/s, from which a mass function of 2.6 +/- 0.3 Msun is obtained. A
revised spectroscopic mass for the WN-type companion of 26+7-5 Msun yields a
black hole mass of 20 +/- 4 Msun for a preferred inclination of 60-75 deg. If
the WR star provides half of the measured visual continuum flux, a reduced WR
(black hole) mass of 15 +4 -2.5 Msun (14.5 +3 -2.5 Msun) would be inferred. As
such, #41/NGC 300 X-1 represents only the second extragalactic Wolf-Rayet plus
black-hole binary system, after IC 10 X-1. In addition, the compact object
responsible for NGC 300 X-1 is the second highest stellar-mass black hole known
to date, exceeded only by IC 10 X-1.
