Among copepods, reproduction is facilitated by a combination of sensory modalities, such as mechano– and chemoreception. The role of chemical communication in copepod mate recognition was assessed using behavioural bioassays that were based on precopulatory behaviours of an estuarine harpacticoid, Coullana canadensis, and the sibling species Coullana sp. Intra– and interspecific crosses demonstrated that males recognize genetically distinct conspecific and heterospecific females, indicating that prezygotic isolation remains incomplete. There was no association between the frequency of mate–guarding behaviour and geographic distance between populations of C. canadensis. However, reduced levels of interspecific mate guarding relative to intraspecific frequencies suggest the existence of a species–specific mate–recognition system. Lectins, which possess strong affinities for specific carbohydrate groups, were used to confirm that glycoproteins on the surface of females function as mate–recognition factors. Information regarding the chemical composition of these molecules was derived from observed effects of lectin binding to females on male mate–guarding behaviour. Mate guarding was inhibited within all tested populations when treated with Triticum vulgaris, a lectin that possesses an affinity for carbohydrates of the N–acetylglucosamine group. Surface glycoproteins responsible for mate recognition in the two species of Coullana may be glycosylated with monosaccharides from this group. Differential responses to lectin treatments suggested that composition of the contact chemical cues vary among populations of C. canadensis and between species. Yet, populations that appeared most similar based on shared lectin responses successfully discriminated against each other in mate–selection experiments. These findings indicate that contact chemical cues probably act in concert with additional factors to promote effective mate recognition and thereby contribute to reproductive success.