This document summarizes an experiment to derive tissue culture cell lines that secrete antibodies against sheep red blood cells (SRBCs). Mouse myeloma cells were fused with spleen cells from mice immunized with SRBCs. The resulting hybrids were selected in HAT medium, and clones that secreted anti-SRBC antibodies were identified using plaque assays. Figures 1 and 2 show that the hybrids expressed antibodies from both parental lines and secreted antibodies that could lyse SRBCs. Figure 3 demonstrates antibody secretion patterns on isolectric focusing, while Figure 4 shows inhibition of lysis by anti-IgM antibody. This technique demonstrated the ability to produce predefined antibodies using fused myeloma-spleen cell lines.