Glomerular basement membrane-reactive antibodies in anti-lymphocyte sera: in vitro and in vivo characteristicsTwenty-four anti-human lymphocyte globulin preparations were examined for the presence of glomerular basement membrane-reactive antibodies by means of one in vivo method and two in v i m tests. This seemed of importance, a s it has been shown that these antibodies fix along the glomerular basement membrane and may thus cause glomerulonephritis. The anti-lymphocyte globulins were prepared by immunizing horses with human lymphoid cells from thymus, thoracic duct, lymphoid cell cultures, blood, tonsil and a mixture of lymphoid tissues. Contamination with glomerular basement membrane-reactive antibodies occurred only when lymphoid cells from thymus, tonsil or from a mixture of lymphoid tissues were used for immunization. It seems t o depend on the c k e with which the isolation of lymphoid cells is performed, whether glomerular basement membrane-reactive antibodies will occur. The glomerular basement membrane-reactive antibodies are directed against common antigenic determinants shared by basement membrane, collagen and reticulin. A horse anti-human thymocyte globulin preparation, containing glomerular basement membrane-reactive antibodies in low titer (1 : 320), was tested in vivo in monkeys and chimpanzees during prolonged treatment ( 6 weeks). This did not lead t o a glomerulonephritis caused by a linear fixation of GBM-reactive antibodies along the glomerular basement membrane. Only slight-to-moderate signs of immune complex nephritis were seen in some of these primates immediately after the 6 weeks treatment, which appeared t o be completely reversible in the monkeys within a period of 4 weeks.