Nonhuman terrestrial mammals sniff themselves and each other to decide who is friend or foe. Humans also sniff themselves and each other, but the function of this is unknown. Because humans seek friends who are similar to themselves, we hypothesized that humans may smell themselves and others to subconsciously estimate body odor similarity, which, in turn, may promote friendship. To test this, we recruited nonromantic same-sex friend dyads and harvested their body odor. We found that objective ratings obtained with an electronic nose, and subjective ratings obtained from independent human smellers converged to suggest that friends smell more similar to each other than random dyads. We then recruited complete strangers, smelled them with an electronic nose, and engaged them in nonverbal same-sex dyadic interactions. We observed that dyads who smelled more similar had more positive dyadic interactions. In other words, we could predict social bonding with an electronic nose. In a current ongoing continuation, we are manipulating participant body-odor (using Deo candy), and exposing them to images of potential friends with either congruent or incongruent body-odor, all within an MRI scanner. The contrast of incongruent versus congruent body-odor generated increased activity in the anterior cingulate cortex, precuneus, cuneus and the cerebellum, a brain network previously associated with “self-other” comparisons. We conclude that self-body-odor may provide a template for the social brain, underlying the chemistry in social chemistry.