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Aims. What is the origin of the large-amplitude variability in Wolf-Rayet WN8stars in general and WR123 in particular? A dedicated spectroscopic campaigntargets the ten-hour period previously found in the high-precision photometricdata obtained by the MOST satellite. Methods. In June-August 2003 we obtained aseries of high signal-to-noise, mid-resolution spectra from several sites inthe {\lambda}{\lambda} 4000 - 6940 A^{\circ} domain. We also followed the starwith occasional broadband (Johnson V) photometry. The acquired spectroscopyallowed a detailed study of spectral variability on timescales from \sim 5minutes to months. Results. We find that all observed spectral lines of a givenchemical element tend to show similar variations and that there is a goodcorrelation between the lines of different elements, without any significanttime delays, save the strong absorption components of the Hei lines, which tendto vary differently from the emission parts. We find a single sustainedperiodicity, P \sim 9.8 h, which is likely related to the relatively stablepulsations found in MOST photometry obtained one year later. In addition,seemingly stochastic, large-amplitude variations are also seen in all spectrallines on timescales of several hours to several days.

A 10-hour period revealed in optical spectra of the highly variable WN8 Wolf-Rayet star WR 123