This paper investigates patterns of usage of thanking formulae in the closing section of a corpus of 94 telephone calls made by tenants to a UK housing association. The data suggest that unilateral thanking is the norm when calls are institutionally and interactionally unmarked. In contrast, mutual thanking correlates mainly with the presence of interactional problems of various kinds, or, in a few cases, with features that are not problematic as such, but simply interactionally marked given the nature of the activity. When initiated by agents rather than by callers, thanking is frequently hearable as conveying an apologetic stance. Participants thus seem to orient to different thanking patterns as devices which may be used either to mark the preceding interaction as an instance of ‘business-as-usual’ or, if such is not the case, to restore interpersonal harmony or index awareness that aspects of the preceding interaction have otherwise deviated from situational expectations.