Two lactating Merino ewes, about 5 years old were used to investigate the effect of 1.V. injection of magnesium gluconate into experi mentally hypomagnesaemic ewe on the organic and inorganic constituents in her milk. During the control period, the animals received a Mg deficient ration (0.045 Mg%) plus 3 grams of Mg0. After that, the MgO-supplement was removed to induce hypomagnesaemia. After the Mg-concen tration in blood decreased below 1 mg/100 ml, 50 ml of 5% solution of magnesium gluconate were i.v. injected. During the control period, the Mg- and Ca-levels in blood plasma averaged 2.44 and 10.1 mg/100 ml respectively. During the same period, the milk analysis revealed the following average values: Mg, 20.4; Ca,198.9 mg/100 ml.,fat 7.3; lactose, 4.8 g/100 ml. On the Mg-deficient ration, the Mg-level in blood plasma decreased to 0.88 mg/100 ml with in 6 days. Neither the hypomagnesaemia nor the injection of magnesium did influence the Mg concentration in the milk. The fat content of the milk could not be increased by the mag nesium injection, The Mg-concentration in blo od plasma has been increased following the in jection to a normal level(2.71-2.48 mg/100 ml) which lasted only for about 12 hours.