Abstract Shaw, A.L., Blake, J.P., Narvaez-Solarte, W.V. and Gunawardana, P.K. 2009. Effects of vitamin U on live performance and intestinal tract integrity in broilers. J. Appl. Anim. Res., 35: 1–7. Two 42 d trials were conducted to evaluate the effects of vitamin U (DL-methionine methylsulfonium chloride) on growth performance, feed efficiency and gut integrity in broilers. 384 day-old mixed-sex broilers were randomly allotted to one of six dietary treatments with eight replicates each. In experiment 1, vitamin U was included in the corn-soybean basal diet at 0, 200, 400, 600, 800 or 1000-ppm. In experiment 2 the vitamin was substituted for synthetic DL-methionine in the basal diet on a molecular weight equivalency at 0, 20, 40, 60, 80 or 100%. Bird and feed weights were collected bi-weekly. Intestinal tissue samples were collected and measured from four birds per treatment on d 42. No significant effects (P > 0.05) were found in either experiment on final body weight gain, feed consumption and feed efficiency due to additions of vitamin U. The additions of vitamin U in Experiment 1 failed to improve villi length, villi width or crypt depth of the small intestine. As the amount of the vitamin increased in the diet an improvement was seen in the villi characteristics of the duodenum, jejunum and ileum during Experiment 2, with the greatest effects found in the duodenum. Overall, vitamin U may provide some improvement to villous characteristics of the small intestine and could be substituted for synthetic DL-methionine in the diet without causing any adverse side effects.