AbstractThe effect of a 20% wheat bran dietary supplement on pancreatic growth and on the content and synthesis of pancreatic RNA and DNA was examined in male Sprague‐Dawley rats fed defined diets for 4–5 weeks. Nutrient intake and body weight gain were similar in the control group (fed a fiber‐free diet) and the groups fed the wheat bran supplement. The wheat bran diet produced no significant change in pancreatic weight, protein, RNA content, or DNA content, but was associated with a 28.8% fall in pancreatic DNA synthesis, measured by [3H]thymidine incorporation into DNA, when compared with the controls (p<0.05). When rats were injected with 50 mg/kg of 5‐fluorouracil (two injections, one week apart), those fed wheat bran exhibited a 40.1% increase in pancreatic wet weight (p<0.005) and a 24.5% decrease in RNA content (p<0.001), when compared to controls fed a fiber‐free diet. RNA synthesis, measured by the incorporation of32P into RNA, increased 3.6‐fold in rats fed wheat bran, when compared with controls (p<0.01). These results suggest that wheat bran should be tested further for any inhibitory action on pancreatic carcinogenesis and for its modifying effect on 5‐fluorouracil toxicity.