  We present the results of an optical spectroscopic study of the massive
Wolf-Rayet binary WR137. These data cover the dust-formation maximum in 1997.
Combining all available measurements of radial velocities, we derive, for the
first time, a spectroscopic orbit with period 13.05 +/- 0.18 years. The
resulting masses, adopting i=67degrees, are M(O)= 20 +/- 2 Mo and M(WR)= 4.4+/-
1.5 Mo. These appear, respectively, around normal and on the low side for the
given spectral types. Analysis of the intense multi-site spectroscopic
monitoring in 1999 shows that the CIII5696 and CIV5802/12 lines have the
highest intrinsic variability levels. The periodogram analysis yields a
small-amplitude modulation in the absorption troughs of the CIV5802/12 and
HeI5876 lines with a period of 0.83 days, which could be related either to
pulsations or large-scale rotating structures as seen in the WN4 star EZ Canis
Majoris (WR6).Wavelet analysis of the strong emission lines of CIII5696 and
CIV5802/12 enabled us to isolate and follow for several hours small structures
associated with density enhancements within the wind of the Wolf-Rayet star.
Cross-correlating the variability patterns seen in different lines, we find a
weak but significant correlation between the varability in emission lines with
different ionization potential, i.e. in lines formed at different distances
from the WR stellar core. Adopting a beta wind-velocity law, from the motion of
individual subpeaks we find beta around 5, which is significantly larger than
the canonical value of 1 usually found in O-star winds.
