As expected, treatment had little effect on the concentration of inorganic phosphorus in group A. In group B, treatment caused a rapid increase in the concentration of inorganic phosphorus to a maximum 20min after the start of treatment. This was followed by a slow decrease in the phosphorus concentration to the normophosphataemic range. Our findings confirmed that combined intravenous and oral administration of sodium phosphate in cows with periparturient paresis attributable to hypocalcaemia and hypophosphataemia results in a rapid and sustained increase in serum phosphorus, but not in serum calcium concentration. This modified therapy did not improve the success rate of milk fever treatment and further studies are needed to improve treatment of periparturient paresis.