1. Gammaglobulin metabolism and distribution were studied employing rabbit gammaglobulin (RGG)I(131) 24 times in 13 control rabbits. Similar studies were performed before and during the ananmestic response in 4 rabbits previously sensitized with a polyvalent pneumococcal vaccine. 2. During the ananmestic response, gamma-globulin levels increased from 1.0 to 6.0 gm/100 ml, and the gamma-globulin pool increased from 0.7 to 4.7 gm/kg. There was no change in the intravascular-extravascular partition of gammaglobulin. 3. Gammaglobulin degradation increased from 0.06 to 0.33 gm/kg/day during the 28 days of the immunization period while gammaglobulin synthesis increased even further to average 0.47 gm/kg/day. Following the attainment of ...