The aim of the study was to evaluate the effect on broiler performance of transgenic Bacillus thuringiensis (Bt) corn containing the Cry1A(b) protein compared with the corresponding near isogenic corn and to analyze the degradation of the Cry1A(b) gene in the digestive tract. Ross male broilers (432) were fed for 42 consecutive days with diets containing Bt or isogenic corn. Diet, Bt corn, and the isogenic form of the Bt corn were analyzed for composition and aflatoxin B1, fumonisin B1, and deoxynivalenol contents. Broiler body weight and feed intake were recorded at regular intervals (d 0, 21, and 42). The presence of the Cry1A(b) gene and plant-specific genes Zein and Sh-2 in gut contents of crop, gizzard, jejunum, cecum, and samples of blood was determined in 10 animals per treatment at the end of the trial using a PCR technique. Chemical composition was not different between Bt and its isogenic form, whereas the fumonisin B1 content for Bt was lower than for isogenic corn (2,039 vs. 1,1034 ppb; P < 0.05). The results of the growth study showed no difference for average daily weight gain (129.4 vs. 126.0 g/d), feed intake (63.4 vs. 61.8 g/d), and feed conversion ratio (1.95 vs. 2.02) among the groups. No significant relationship was observed between mycotoxins content and growth performances. Feed-derived DNA is progressively degraded along the digestive tract. Detection frequency of short fragments of maize-specific high copy number Zein gene was high but significantly decreased in distal sectors. An 1,800-bp fragment of the Cry1A(b) gene, corresponding to the minimal functional unit, was detected only in crop and gizzard of birds fed Bt corn. Sh-2 showed the same detection frequency of Cry1A(b) and was also found in birds fed isogenic corn. Blood samples were positive with low frequency only for the Zein gene fragment. No significant difference in DNA detection was observed between birds fed Bt and isogenic corn, indicating that DNA derived from transgenic feed undergoes the same fate as isogenic feed.