Social relationships can be described by a series of components, all having putatively different functional roles in the lives of humans and other social species. For instance, certain relationship characteristics can strongly influence how individuals deal with stress, ultimately influencing their fitness. However, species vary highly in regard to which components of their relationships influence stress buffering and how. Variation in species' social organization could explain such differences. Comparing closely related species subjected to different ecological constraints can be especially informative when investigating this hypothesis. Here, we compared whether relationship quality differently influences how grey wolves, Canis lupus, and domestic dogs, C. l. familiaris, react to a series of stressors. We tested the role of various relationship components (i.e. two affiliation indices and two aspects of dominance rank) in mediating stress reactivity, social support seeking and social referencing in dyads of pack-living animals. To do so, we conducted systematic long-term observations of the social interactions between animals and an experimental test battery exposing animal dyads to a series of stressors (e.g. novel environment exploration, separation from and consequent reunion with the partner, exposure to a novel object and a threatening human). We found that a large rank distance and high affiliation index based on the number of friendly behaviours exchanged during everyday life (but not dominance status or the affiliation index based on the time spent in body contact) were related to a dampened stress response in both species. These results suggest a functional role of these two relationship components in the stress buffering of both dogs and wolves. (c) 2021 The Authors. Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).