AbstractIntroductionPeer‐related interpersonal stress can increase risk for suicidal thoughts among adolescents and young adults. However, not all individuals who undergo peer‐related interpersonal stressors experience suicidal thoughts. Heightened proinflammatory activity is one factor that may amplify the relation between interpersonal stress and suicidal thinking.MethodsThis pilot study examined the relation between interpersonal stress and suicidal ideation in real time, as well as whether proinflammatory cytokine (IL‐6 and TNF‐α) activity across a laboratory social stressor moderated this association in a sample of 42 emerging adults with recent suicidal ideation. Participants completed 28 days of 6×/daily ecological momentary assessment that assessed for suicidal ideation (presence vs. absence, ideation intensity), occurrence of negative peer events, and feelings of exclusion.ResultsThere was a trend for within‐person increases in feelings of exclusion to be associated with increases in concurrent suicidal ideation intensity. Additionally, within‐person increases in negative peer events were associated with increased odds of subsequent suicidal ideation among individuals with very low IL‐6 activity. However, this finding is considered preliminary.ConclusionInterventions targeting perceptions of exclusion and increasing social support may be of benefit. However, findings require replication in larger samples, and thus must be interpreted with caution.