From 50 Friesian heifers (9 months) at Bani-Mour station 10 animals showed nervous manifestations which include hyperasesthesia, tetany and incoordination. Hypomagnesaemia was incriminated as the main cause for the previous clinical signs. Our suspecion was confirmed after blood analysis as hypomagnesaemia associated with hypocalcaemia was recorded. The diseased animals were treated by 10% magnesium sulphate and mineral salt administration. The haemogram of diseased animals was discussed before and after treatment. Application of the treatment revealed that abnormal clinical signs had disappeared as well as blood biochemical changes returned normal. The study also revealed that hypomagnesaemic tetany can be controled by feeding magnesium supplements to prevent the seasonal fall in serum magnesium levels.