1. Gamma globulin metabolism and distribution were studied employing rabbit gamma globulin (RGG)I131 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 gamma globulin.
3. Gamma globulin degradation increased from 0.06 to 0.33 gm/kg/day during the 28 days of the immunization period while gamma globulin synthesis increased even further to average 0.47 gm/kg/day. Following the attainment of elevated gamma globulin levels the fractional rate of RGG-I131 turnover increased from 8.0 to 12.5 per cent/day.
4. No differences were noted in the metabolism of homologous or autologous gamma globulin regardless of the allotypic specificities.