Antilymphocyte antibodies have been found in patients with systemic lupus as well as other connective tissue diseases. We have described a high incidence of these antibodies in asymptomatic relatives of SLE patients. These studies suggest that antilymphocyte antibodies may be a useful marker of an environmental agent important in the pathogenesis of these diseases. During the next year, I plan to study the specificity of these antibodies using cultured cell lines as targets and a variety of antisera with known specificity as blocking agents. We have recently described a glass adherent prostaglandin producing suppressor cell in man. Its role as a possible cause of decreased T cell function will be examined in a variety of clinical conditions.