Distance Wagner networks are unrooted trees which can be used to indicate the relationships between taxa. They are converted into trees or cladograms by being given a root and thus provide one of the techniques of numerical cladistics (Farris, 1972). These networks not only enable one to hypothesize the branching sequence but also the relative extent of anagenesis. These networks can be constructed from continuous and meristic morphometric characters. When morphometric data are used there is disagreement as to the appropriate coding procedure. There has been insufficient analysis of the influence of character coding on these networks and Colless (1980) considers whole area has been poorly investigated. Johnson and Mickevich (1977) used gap-coding on their six morphometric characters to convert them to ordinal multistate characters. These were then transformed to binary variables by additive coding. Riska (1979) points out some potential difficulties in comparing evolutionary rates of gap-coded characters, while Colless (1980) regards gapcoding as arbitrary and suggests range coding as an alternative. In reply, Mickevich and Farris (1981) have criticized range coding because it treats all characters as if they have evolved the same amount. However, some overt decision about coding is necessary if the characters have been recorded in different or arbitrary units. This paper attempts to indicate the influence of different coding methods on Distance Wagner networks. The data set is based on a large number of morphometric variables recorded from populations of the western grass snake, Natrix natrix helvetica (Lacepede). This is one of the four semispecies of the grass snake species complex. The systematics of this species complex have been the subject to a series of investigations based on multivariate morphometry (references in Thorpe, 1980). The causative factor for the main phenetic pattern of geographical variation is thought to be historical (microphylogenesis) rather than adaptation to current ecological conditions (Thorpe, 1979) and subsequently Distance Wagner networks have proved extremely useful in understanding the phylogeny and range expansion of the species complex (Thorpe, 1982, 1983, 1984). This has enabled a decision to be made between a primary or secondary origin for the transition (hybrid) zones within the species. Numerical cladistics have also proved useful for investigating variation in other species where the OTUs may be smaller units, i.e., demes (Johnson and Mickevich, 1977) or larger units, i.e., subspecies (Loudenslager and Gall, 1980) than the compound localities used in this study. It is not only the network configuration that is of interest at this level but also the relative extent of anagenesis (Thorpe, 1982, 1983, 1984). The ability ofthe coding procedure to differentiate between the populations is also pertinent because if one cannot differentiate between populations some critical phylogenetic information can be lost, as for example, in the study of range expansion in the eastern grass snake (Thorpe, 1984).