Lewis (LEW) rats immunized with Brown Norway (BN) rat renal basement membrane (RBM) and adjuvants produce high titer circulating anti-BN tubular basement membrane (TBM) antibodies, in addition to developing an autoimmune cell-mediated form of nodular tubulointerstitial nephritis (TIN). This immune LEW serum, which reacted with BN TBM but not LEW TBM by immunofluorescence, was capable of passively transferring TIN as early as 24 hr after administration of volumes as low as 3 ml i.v. to normal BN recipients, producing focal lesions histologically and immunopathologically similar but less extensive than those studied previously in this strain after active immunization with heterologous RBM. In contrast, a total of 45 ml of serum (in multiple doses) from BN rats immunized with bovine RBM and adjuvants produced only one small lesion of TIN in a recipient BN rat. This difference in serum transferability of anti-TBM-associated TIN appears to relate to quantitative differences in anti-particulate and soluble (collagenase-extracted) BN RBM antigen reactivity measured by radioimmunoassay. Paired-label quantitative studies of passively transferred LEW anti-BN RBM IgG demonstrated a slow accumulation of renal-bound antibody over 6 days, and corresponded with kidney elution and immunofluorescence studies after transfer of immune LEW sera to normal BN rats. Approximately 167 micrograms of kidney-fixing antibody per gram of kidney were calculated to be required for the development of the earliest cellular infiltration. C3 depletion with cobra venom factor greatly diminished the development of destructive TIN lesions associated with multinucleate giant cells after passive transfer of LEW anti-BN RBM antibody to BN rats. This study, using immune LEW sera containing high levels of anti-BN RBM antibody, has defined and quantitated a role for anti-TBM antibody and complement in the initiation of TIN in BN rats.