The general objective will be to gain a greater understanding of immune responses by studying less complex model systems than ourselves. During the past several years I have been visualizing erythrocyte responses in representatives of three groups of Amphibia (Triturus viridescens, Xenopus laevis and Rana pipiens) which demonstrate different levels (functional, developmental and anatomical) of sophistication in immunity. During the coming year my interest will continue to focus on questions relating to the antigen binding specificity of individual immunized lymphocytes. Since the coming year is my sabattical leave time, studies which have now shown that primitive, but not advanced, amphibia do not have phenotypic restriction of individual lymphocyte specificities will be extended to fish at the Hall Institute at Melbourne, Australia with Dr. J. J. Marchalonis. Additionally, since quantitation of various aspects of the immune response requires study in vitro, the second half of my leave will be in the laboratory of Dr. M. Balls, University of Nottingham Medical College, England, where amphibian tissue culture work is actively carried on.