Summary Agglutinin and hemolysin titers have been obtained from extracts of washed cells secured from selected lymph nodes and thymi of mice immunized to sheep erythro-cytes. The titers of similar extracts of salivary glands and muscle of the same immunized animals were negative in all dilutions although these extracts were higher in nitrogen content. Per unit of extractable nitrogen, lymphoid tissue had significantly higher agglutinin and hemolysin titers than did the sera of the same animals. It is concluded that antibodies are concentrated in lymphocytes.