There is strong epidemiological evidence that more physical activity is associated with reduced risk of colon cancer, but the amount or type of activity necessary to invoke this protection is disputed, and the mechanism that is responsible has not been elucidated. The present study compared the effects of two contrasting exercise regimens on intestinal tumourigenesis in Min mice, and investigated two novel mechanistic factors: colonic butyrate and sleep. From 5 weeks of age, Min mice were exercised by running on a treadmill (TR; < or = 21 m/min, 30-60 min/d, 5 d/week, < or = 12 weeks). Additional groups of mice were provided with an exercise wheel (WH) or no exercise (CON). Mice had free access to a Western-style, high-fat diet. WH mice ran 3.97 km (females) and 1.92 km (males) daily (P = 0.002). There were no differences in body weight gain or body composition between treatment groups. Treadmill running reduced the numbers of larger ( > or = 2 mm diameter) tumours (P = 0.042), and tended to reduce tumour multiplicity in the colon (P = 0.049). TR mice had a higher molar proportion of butyrate in colonic digesta than CON mice (P = 0.030), and when treatment groups were combined, there was a weak negative correlation (r - 0.174, P = 0.061) between butyrate molar proportion and total tumour number. In a subset of animals in which non-exercise physical activity was monitored, there were strong positive correlations between sleep duration and both tumour multiplicity (P < 0.001) and tumour burden (P = 0.001). More studies of the effects of sleep and of colonic butyrate in mediating the effects of physical activity on intestinal tumourigenesis are warranted.