Summary: Evidence was presented that primary chicken anti-bovine serum albumin (BSA) antisera contain a high molecular weight antibody which precipitates in 0.15 M NaCl and which agglutinates sensitized red cells, a 7 S non-hemagglutinating antibody which precipitates only in 1.5 M NaCl when isolated from the heavier fraction by zone ultracentrifugation, and a 7 S hemagglutinating antibody which precipitates in 0.15 M NaCl and which is also found in high concentrations in hyperimmune sera.