We administered bovine serum albumin (BSA) 1 or 3 mg i.v. into hyper-immune Sprague-Dawley rats weekly for up to 6 months. Animals with free circulating antibody 1 h after BSA developed mesangial deposits of IgG and C-3 without proteinuria. Rats without free antibody at 1 h developed either mesangial or mesangial and glomerular basement membrane (GBM) deposits. Rats given 3 mg BSA tended to have GBM deposits, proteinuria and undetectable antibody at 1 h. By electronmicroscopy, all rats had mesangial and subendothelial dense deposits, while those with GBM lesions had intramembranous and subepithelial deposits with foot process obliteration. Light microscopic evaluation of kidney tissue revealed only mild histological changes similar to those in age-matched control rats. The present studies demonstrate that prolonged i.v. administration of BSA into rats results in the development of a chronic non-inflammatory nephropathy. Despite certain parallels to chronic serum sickness nephropathy in rabbits, species differences appear to modify the nephropathy in rats.