Objective: To better understand age and gender differences in associations of social relationships with chronic inflammation. Method: Using a sample of middle-aged and older adults ( N = 963) from the Midlife Development in the United States (MIDUS) biomarker project, we examined interactions of age and gender with structural and functional social network measures in predicting interleukin-6 (IL-6) and C-reactive protein (CRP). Results: Significant interactions involving age and gender showed that social support was associated with lower IL-6 in older women, whereas perceived positive relationships and social integration were related to lower IL-6 in both men and women of advanced age. Functional measures were associated with higher CRP in both men and women after adjustment for health conditions and behaviors, with some further variation by age. Discussion: Greater social support may be related to lower IL-6 in older women. Further research is needed to understand observed associations of social support with higher CRP.