The set of monoclonal antibodies prepared against rabbit lymphocytes has been used in two separate types of experiments. The cell-surface molecules recognized by these antibodies have been isolated and primary structural studies have begun on several of them. In addition, their ability to recognize cell subpopulations have been useful both in preparative separation of normal rabbit lymphocytes and in functional analysis of rabbit T cell lines and clones specific for streptococcal antigens. An ELISA for anti-streptococcal antibody has been developed to facilitate characterization of these rabbit T cell lines. In separate experiments, hamster female protein, an acute phase protein under sex hormone control has been characterized by primary structural analysis at the protein level and preliminary studies at the DNA level. Messenger RNA has been prepared and cloned in an effort to complete the structural studies and to understand the hormonal regulation of this gene.