1. One thousand Silver Grey Hyline hens were given drinking water containing 5 concentrations of added sodium fluoride (0, 6, 10, 14 and 20 mg/l) over a 17-week growth and 57-week laying period. The natural fluoride content of the water was 0.21 mg/l during the growing period and 0.29 mg/l throughout lay. 2. During the rearing phase, efficiency of food utilisation and mortality were not significantly affected by the fluoride concentration of the water. Weight gain and food intake decreased in the 10 and 14 mg/l fluoride treatments. 3. During the laying period, the fluoride content of the water had a significant effect on egg production, but eggshell breaking strength was not significantly influenced. 4. Post mortem analyses, carried out at the end of lay (74 weeks of age), showed that carcase weight and the fluoride content of the os femur increased significantly as the fluoride concentration in the water increased; the increase in bone fluoride followed a linear pattern. 5. Histopathology showed no evidence of changes in the livers or kidneys; liver weights and breaking strength of the os femur were unaffected by the amount of fluoride consumed. 6. The data showed that under commercial conditions, laying birds can tolerate ingesting 4.453 mg fluoride/day for up to 74 weeks.