Previous research suggests that some individuals of the red-backed salamander (Plethodon cinereus) in Virginia form socially monogamous relationships. We investigated if living together for 9 d is sufficient to establish such a relationship. In our first laboratory experiment, we tested two hypotheses: that increased familiarity between territorial males and female intruders would lead to (1) reduced aggression and (2) increased touching (conciliation) by the males, as expected in social monogamy. We posed the same two hypotheses in our second experiment for territorial females responding to male intruders. When residents and intruders first met, residents in both experiments spent more time in threat postures than they did 9 d later. Thus, familiarity led to decreased aggression toward intruders of the opposite sex. We then removed the now familiar first intruders and replaced them with unfamiliar second intruders. Aggression by residents in both experiments increased, suggesting that male and female residents can distinguish between a familiar and an unfamiliar intruder of the opposite sex. When we shortly thereafter removed the second intruders and, 2 d later, reintroduced the original first intruders, in both experiments residents maintained low levels of aggression. This suggests that they could remember the first intruders after 2 d of separation, even with the intervention of an unfamiliar member of the opposite sex. We found no difference in touching behavior for residents in either experiment. Thus, our first hypothesis (concerning reduced aggression) was supported while our second hypothesis (concerning increased touching) was not. Therefore, the formation of socially monogamous relationships may require longer than 9 d of living together and/or a ‘choice’ of partners, which would be possible in the natural habitat but was randomized in our experiments.