Progressive proteinuria has been suggested not just to reflect but also to contribute to the development of focal glomerular sclerosis. Development of proteinuria and glomerular lesions was examined up to 18 weeks after 3/4 nephrectomy in Sprague-Dawley (SDR) rats and an analbuminemic SDR variant (NAR). Nephrectomy led to a significantly lesser degree of proteinuria in NAR (42 +/- 14 SD mg/day) than in SDR (140 +/- 54 mg/day), consistent with the fact that 50-60% of urinary protein in SDR after nephrectomy is serum albumin. Nevertheless at 18 weeks NAR showed a significantly higher frequency of moderate and severe glomerular lesions than SDR. We conclude that, in this model, proteinuria itself is not a major cause of progressive glomerular injury.