Summary.A study is made of the changes in the ascorbic acid content of the corpus luteum of pregnancy in the rabbit (12th day of pregnancy) at varying times (45 minutes to 48 hours) after the intravenous administration of 450 I. U. of pregnant mare serum gonadotrophn (PMS).Gonadotrophic stimulation gives rise to changes in the weight of the corpus luteum (+ 39 per cent after 12 hours, – 18 per cent after 48 hours). This fact must be taken into consideration in the calculations of the ascorbic acid content.Gonadotrophic stimulation causes a rapid, relatively considerable fall in the ascorbic acid content,i. e.10 per cent after 45 minutes, 22 per cent after 11/2hours and 25 per cent after 3 hours. This is followed by a considerable increase, with a maximum 24 hours after stimulation.Pregnant mare serum gonadotrophin is considered to affect the corpus luteum either directly or indirectl