Pro-inflammatory cytokines are produced as part of innate immunity. Increased resistance to extraintestinal Salmonella enteritidis (SE) has been associated with an increase in heterophil pro-inflammatory cytokine gene expression. Invasion of chicken epithelial cells by SE induces an 8- to 10-fold increase in interleukin (IL) -6 production. Infection with SE induces an influx of heterophils to the site of infection; therefore, we hypothesize heterophils would be responsive to IL-6. The objective was to determine the effects of COS cell-derived recombinant chicken interleukin 6 (rChIL-6) on in vitro functional activity of heterophils. Heterophils were incubated with rChIL-6 or mock-transfected COS cell supernatant and functional activity was assessed. Heterophils treated with rChIL-6 showed no functional differences compared to controls. These data indicate rChIL-6, alone, does not affect the functional activity of neonatal chicken heterophils in vitro. Therefore, the function of IL-6 in the local environment in response to SE invasion is still unknown.