Intramuscular injections of 4 or 8 mg 25-hydroxycholecalciferol (25-OH D3) in 5 ml corn oil given three days before the predicted calving date and repeated at weekly intervals until calving effectively reduced the incidence of parturient paresis. Drug efficacy was improved in cows receiving low to normal recommended levels of dietary phosphorus prepartum. With proper management techniques, 25-OH D3 could prevent parturient paresis in dairy cattle.