This article deals with the marking of grammatical relations in Tariana, North-Arawakan, and how this marking interrelates with topicality, definiteness and other discourse characteristics of nominal constituents. The following four case-marking systems are distinguished in Tariana: (i) a subject vs object case system, used with personal pronouns with animate reference; (ii) a case system characterized by an enclitic -nuku for marking topicalized and referential non-subjects, used with all types of nominal constituents; (iii) an ergative case-marking used with all types of nominal constituents under emphasis in A function, the ergative case marker being the same as instrumental; (iv) a system of peripheral cases – locative and instrumental, used with all types of nominal constituents, but obligatory only with pronouns. The overt case-marking in Tariana is related to such parameters as topicality, definiteness and emphasis, and consequently is dependent on the structure of discourse. I will argue that the unusual case-marking patterns in Tariana corroborate cross-linguistic generalizations on a dependency between case-marking and topical properties of NPs in languages with an opposition between marked and unmarked case forms.