The taxonomic status of Microtus guentheri, which is distributed in Anatolia, and the related taxa (number of chromosomes 2n = 54) inhabiting Western Anatolia and Southeast Thrace within the territory of Bulgaria and Turkey, were investigated morphologically and statistically. It was determined that the form of the second upper molar in all studied M. guentheri specimens belonged to the non-agrestis morphotype as did that in all specimens from Western Anatolia, Bulgarian and Turkish Thrace. The forms of the third upper molar did not separate M guentheri from the specimens of Western Anatolia, Bulgarian and Turkish Thrace, and showed great variations among the normal, simplex, duplicate, and complex forms. In contrast, the marked distinguishing characteristics in dorsal colours, and skull and baculum morphologies were found between these populations. Statistical analyses (Tukey HSD) showed that the mean values of 18 variables in Thrace specimens and M. guentheri and 23 variables in the specimens of Thrace and Western Anatolia were significantly (p<0.05) different one from another. According to Principal Component Analyses, 75% of the total variance was explained by five components that had eigenvalues higher than 1, and specimens of Bulgarian and Turkish Thrace were clearly separated from M. guentheri and the specimens of Western Anatolia in discriminant function analyses. These findings suggested that specimens from Bulgarian and Turkish Thrace cannot be identified as M guentheri. According to the priority rule, the specimens from Bulgarian and Turkish Thrace were assigned to Micron's hartingi and the subspecies martinoi and strandzenzis were considered junior synonyms of this taxon. However, the strong morphological and statistical evidences were provided the population in western Anatolia should be assigned to Microtus lydius as a valid species.
