A chronic renal disease was induced by 5/6 nephrectomy in young adult Wistar albino male rats. Groups of 3 rats were killed at varying time intervals from 10 to 50 weeks after nephrectomy, and the glomerular structure was studied by light and electron microscopy. By light microscopy, increase in glomerular size and hypertrophy of the visceral glomerular epithelial cells were evident as early as the tenth week. Significant degree of glomerular hyalinization started on the 25th week and gradually became more extensive in involvement towards the 50th week. By electron miscroscopy, the hypertrophied glomerular epithelia showed many osmiophilic bodies and vacuoles in their cytoplasm and fusion of foot processes. Beginning on the 30th week, increase of the mesangial matrix was quite evident, and endothelial and epithelial cells disappeared from the areas where the increase was prominent. The increased matrix gradually encroached and occluded capillary lumina and Bowman's space, leading to a formation of obsolescent glomeruli. Whether or not these glomerular changes are due to the glomerular hyperfiltration which has been known to occur after 5/6 nephrectomy remains to be elucidated.