The mechanisms responsible for the evolution of antibodies, a multigene system, will be studied by the comparative amino acid sequence analysis of homogeneous and normal immunoglobulins from rabbit (mammal), chicken (avian) and shark (elasmobranch). The automatic protein sequenator permits the rapid analysis of portions of many proteins and large peptide fragments and, accordingly, will enable us to determine the extent and patterns of variability for selected portions of light and heavy immunoglobulin chains. The nature of evolutionary changes in variable and constant regions will be compared to further characterize the evolution of this multigene system.