We have removed the spleen and auto transplanted in 49 rabbits, varying in age from 26 days to over two years.The method consists of introducing a small fragment of spleen, roughly 2-3 mm. in diameter, beneath the subcutaneous fascia of the abdomen, through a skin incision which is then closed by suture. These transplants have been subjected to direct examination at approximately monthly intervals to check their taking, growth or absorption. All have taken, except for three instances and these failures were due to infection. The most striking observation was the rapid growth of the grafts in the young rabbits from one to three months old and the lack of growth in the one- and two-year-old rabbits, some of which have undergone complete absorption in three months, as shown by histological examination. On the other hand, none of the transplants in rabbits less than five months old have shown any tendency to undergo absorption and histological examination shows regeneration of the major splenic elements into ...