Mechanisms involved in the pathogenesis of necrotizing enterocolitis (NEC) are not well understood. Prematurity, ischemia, presence of bacteria and substrate in the intestine have all been implicated in this disease process. The role of bacteria in eliciting a proinflammatory cytokine response has been widely reported, and elevated levels of IL-1β, IL-8 and IL-6 have been demonstrated in blood and tissue samples from babies with NEC. In the current study, we examined the expression of cytokine mRNAs in response to defined bacterial insults in the rabbit gut. An E. coli strain was used to produce NEC-like injury in the weanling rabbit ileal loop model using our previously reported protocols (Pediatr Res 36:115-21, 1994). Control and diseased ileal tissue samples were obtained from multiple loops in 4 rabbits 16-24 hours after bacterial infection and quickly frozen in liquid nitrogen for RNA extraction and further analysis. Expression of cytokine mRNAs was examined by Reverse Transcriptase- Polymerase Chain Reaction using rabbit-specific primers and quantified in a fluorimager. Each cytokine was normalized against β-actin. There was a significant increase (p<0.05) in the expression of IL-8 in infected loops. The mean value of IL-8 in E. coli infected loops was 0.34 (SEM 0.05) compared to 0.19 (SEM 0.04) in controls [p < 0.05]. For IL-1β, the mean value was 0.21 (SEM 0.09) compared to 0.12 (SEM 0.05) in controls [p = NS]. In contrast to the increased expression of IL-8 and IL-1β, the infected loops had a value of 0.16 (SEM 0.04) compared to 0.19 (SEM 0.05) in uninfected controls for IL-6 [p= NS]. Although IL-6 has been implicated in inflammatory states, its inhibitory effect on TNF and IL-1β has also been reported (Aderka et al.J Immunol 143:3517-23, 1989; Barton et al. Infect Immun 60:749-53, 1992). Failure to upregulate IL-6 as observed in our system may potentiate proinflammatory cytokines and may contribute to the pathogenesis of NEC.