1. Rabbits that had received repeated intravenous injections of heat-killed indifferent streptococci with no resulting sensitization were subsequently made skin-sensitive to them by repeated intracutaneous injection of heat-killed vaccine.
2. Serum agglutinins and precipitins developed earlier in rabbits that had received repeated intravenous injections of killed streptococci and pneumococci than in those injected intracutaneously. However, when such injections were continued over a longer period, the antibodies in both groups of animals reached a similar level.
3. Species specific agglutinins reached about the same level after either intracutaneous or intravenous injections of heat-killed Type I(S) pneumococcus vaccine. Type specific agglutinins were present only in the intravenously injected animals after 33 days but were present in all the animals after 63 days although the titres were somewhat lower in those injected intradermally. Both groups developed precipitins which were only slightly less in the intradermally injected rabbits.
4. These experiments indicate that rabbits intravenously injected with heat-killed streptococci can be made highly skin-sensitive in the same manner as animals injected intracutaneously and that they are not immune or refractory to skin sensitization. When antigen was injected either intracutaneously or intravenously into rabbits for a fairly long time, the amount of circulating antibody in both groups was approximately equal.