Abstract
Antiserum was made in rabbits to a cell extract of stage 12 Rana pipiens embryos. The re-aggregation of dissociated cells of Rana ectoderm and endoderm was inhibited by the antiserum. The antiserum had no effect on the reaggregation and segregation of dissociated cells of Triton alpestris embryos. The role of antigen-antibody-like reactions in cell adhesion is discussed.