Zinc sulfate (ZnSO4) was added to the diet of adult ewes and lambs with contagious foot rot for periods of 4 weeks to 6 months and to the diet of lambs for 5 weeks before experimental exposure to foot rot. Intake averaged between 0.5 and 0.75 g/animal/day. A beneficial effect was demonstrated when lambs with foot rot were fed ZnSO4 and were maintained under dry conditions, but when conditions were wet, ZnSO4 did not reduce the number of infections or prevent new infections. When ZnSO4 was fed before exposure, the infection rate of medicated lambs in a wet environment was almost twice that of unmedicated lambs in the same pen.