It is shown that morphological characters, such as a form of gnathosoma, usually considered as qualitative one, may be properly analyzed on a quantitative basis by means of the geometrical morphometric methods. In particular, an extraction of relative warps (RW) from a shape variation using TPSRW computer program makes it possible to run standard statistical procedures over matrices of RW values. This approach is demonstrated by the analysis of gnathosoma shape differences in 4 Ixodes species and 3 Dermacentor species, with a discriminant analysis being employed as a statistical routine. It is shown that differences among I. persulcatus and I. ricinus are statistically significant (by F-criterium) in all ontogenetic phases, while in the case of I. laguri and I. redikorzevi this is true only for the larval phase. Magnitudes of the gnathosoma shape variation among species (by F criterium) are similar within both Ixodes (s, str.) and Serdjukovia subgenera. The differences among subgenera of the genus Dermacentor are more significant.