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We present the results of a systematic search for large-scale spectroscopicvariability in apparently single Wolf-Rayet stars brighter than ~12.5. In thisfirst paper we characterize the various forms of variability detected anddistinguish several separate groups. For each star in our sample, we obtained4-5 high-resolution spectra with a signal-to-noise ratio ~100. Our ultimategoal is to identify new candidates presenting variability that potentiallycomes from Co-rotating Interaction Regions (CIR).  Out of a sample of 25 stars, 10 were found to display large-scale changes ofwhich 4 are of CIR-type (WR1, WR115, WR120 and WR134). The star WR134 wasalready known to show such changes from previous studies. Three WN8 starspresent a different type of large-scale variability and we believe deserve agroup of their own. Also, all three WC9d stars in our sample presentlarge-scale variability, but it remains to be checked if these are binaries, asmany dust-making WR stars are double. Finally, of the remaining stars, 10 werefound to show small-amplitude spectral changes which we attribute to normalline-profile variability due to inhomogeneities in the wind, and 5 were foundto show no spectral variability, as far as can be concluded from the data inhand.  Follow-up studies are required to identify potential periods for ourcandidates showing CIR-type changes and eventually estimate a rotation rate forthese WR stars.

A Systematic Search for Corotating Interaction Regions in Apparently Single Galactic WR Stars. I. Characterizing the Variability