Both transgenic plant gene fragments were found in the gastric VE-821 digesta of 90% of the pigs fed Bt maize either for the entire 110 days or only for the final 80 days of the study. Faint signal bands for both cry1Ab-1 and cry1Ab-2 were detected in gastric digesta of 40% of the pigs fed either GW786034 isogenic or Bt/isogenic maize diets, respectively at slaughter on day 110. This is thought to have occurred due to sample contamination post-sampling. No Bt toxin fragments were detected in gastric digesta from these pigs. Likewise, cry1Ab gene contamination was not found in other digesta samples from these pigs and prior to feeding, no cry1Ab gene fragments were detected in the isogenic maize. The cry1Ab-1 gene fragment was detected in the ileal digesta of 20 and 10% of the pigs fed Bt maize for the entire 110 day period and the final 80 days of the study, respectively. However, the cry1Ab-2 gene fragment was not detected in the ileal digesta of any pigs fed Bt maize at any time. Likewise, no transgenic plant gene fragments were detected in the cecal or colon digesta of pigs fed Bt maize for 80 or 110 days. All digesta samples from pigs fed the isogenic maize diet for 110 days or Bt/isogenic maize diets did not contain either transgenic plant gene fragment. The Bt toxin was not detected in the kidneys, liver, muscle or in the sera of any of the pigs fed any of the four dietary treatments at any time point during the study. The Bt toxin was not detected in the stomach, cecal or colon digesta of pigs fed the isogenic maize diet or pigs fed the Bt/ isogenic maize diet. It was only detected in the digesta of pigs fed Bt maize for 110 days or the isogenic/Bt maize diet. In these pigs, it was detected in 90 and 80% of the gastric samples, 80 and 50% of cecal samples and 100% of colon samples, respectively 3 h after the last meal was administered. The mean concentration of Bt toxin was lower in the digesta of pigs fed the isogenic/Bt maize diet compared with those fed Bt maize for the entire study period, except in the cecum where the opposite was true. In both Bt maize-fed groups, the mean concentration of Bt toxin in the cecal digesta was lower than in the gastric or colon digesta. In fact, the Bt toxin was most concentrated in the colon digesta. To our knowledge, this study is the first to evaluate the effects of long-term feeding of Bt maize on peripheral immune response of pigs. It is also the first to investigate if age at feeding impacts the response in pigs. By using a cross-over study, we were able to evaluate any residual effects on peripheral immune response that may emerge in older pigs having received Bt maize for a relatively short time period in early life as well as the effects of feeding Bt maize for a longer period later in life. Changes in peripheral immune response were evaluated through measurement of cytokine production from PBMC, investigation of Cry1Ab-specific antibody production in serum, immunophenotyping and haematological analysis.