The effect of consumption for 24 weeks of different amounts (0%, 5% or 10% w/w) of fermentable (pectin and guar gum) or nonfermentable (cellulose and lignin) dietary fibres on cell proliferation and other parameters in large bowel mucosal crypts was studied in rats. In all 12 dietary groups, the crypts located over the distal aggregate of lymphoid nodules (ALN) had more colchicine arrested metaphase figures per midaxial crypt section (MC) and a longer crypt column height than crypts located three to four cm away from this ALN. These differences are attributed to the tropic influence of nodular cells in the ALN. Consumption of fermentable fibre decreased pH in the lumen of the caecum, and glucose, Zn and Cu in serum but increased Ca and Mg in serum. The decrease in caecal pH and serum glucose was significantly correlated with a decrease in MC. Increased intake of the nonfermentable fibre types increased faecal bulk but had no significant correlation with the other measured crypt parameters. Multiple regression analyses was used to model the relationships between the mucosal crypt criterion variables and the two measured predictor variables, caecal pH and serum glucose. Relationships between dietary fibre, ALN, MC, bioavailability of dietary minerals and risk of colorectal cancer are discussed.