Laboratory experiments were carried out to test the effect of dietary supplements of fresh sprouted wheat on reproduction of the Bank vole, Clethrionomys glareolus. One hundred and twenty females were divided into three groups at weaning: (a) group NSS (no sprout supplement), (b) group LSS (low sprout supplement) and (c) group HSS (high sprout supplement). Six- to seven-week-old females were paired with fertile males. Both groups on sprout supplement showed a significantly higher incidence of pregnancy in primiparous females (76%) compared with controls (NSS) (46%). Diet had no significant effect on the incidence of pregnancy in multiparous females. Control females had consistently higher mean litter sizes up to and including the fifth litter, compared with experimental females. Primiparous NSS females had the highest mean litter size and the experimental group HSS had the lowest. Differences in mean litter interval between groups were related to litter size (number of sucklings) rather than diet. The number of foetuses in utero had no effect on litter interval. The incidence of post-partum conception was higher in group LSS as compared with groups HSS and NSS. Diet did not affect the mean number of young produced per female in a given time, or the percentage of young surviving to weaning. The results are discussed with reference to their implications regarding habitat suitability of C. glareolus.