A secondary pilot study was carried out as part of a larger parent study of thyroid function in pregnancy and postpartum. All women in the parent study (N = 631) had blood samples, demographic data, and measures of perceived stress and dysphoric moods collected between 16 and 26 weeks' gestation. The current study was completed with a subset of 105 pregnant women to examine the relationships among perceived stress, depression, plasma cortisol, and cytokines during the second trimester of pregnancy. Stress was measured using Cohen's Perceived Stress Scale and dysphoric moods using the Profile of Mood States Depression/Dejection Scale. Cytokines were measured by a 12-plex analysis on a Luminex-200, and cortisol was measured by enzyme-linked immunosorbent assay on stored plasma samples. Stress and depression scores were highly correlated, and depressive symptoms were inversely correlated with 3 of the 12 cytokines: interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and IL-7. Cortisol was inversely correlated with proinflammatory cytokines (IL-1β and TNF-α) and anti-inflammatory cytokines (IL-4, IL-5, IL-10, and IL-13). These data support the new conceptualizations of normal pregnancy as an inflammatory state that is carefully regulated, as both excessive and inadequate inflammation are potentially hazardous to the health of the pregnancy and fetus.