We performed 308 series renal biopsies during 4 years (1985-1989) and 289 cases were examined by light microscopic, electron microscopic, or immunofluorescent study. Clinically, chronic nephritic syndrome was most frequent (55.4%), followed by nephrotic syndrome (15.1%), and recurrent or persistent hematuria (12.8%). Pathologically, IgA nephropathy was most popular (39.3%), followed by normal glomerulus (9.1%), and thin basement membrane disease (8.7%). Glomerulonephritis clinically recognized with recurrent or persistent hematuria, hardly showing proteinuria, in 81.6% of the cases, consisted of normal glomerulus, or thin basement membrane disease by electron microscopic and immunofluorescent examinations. The remainder (18.4%) was with IgA nephropathy, which was histologically mild. On the other hand, cases of chronic nephritic syndrome (latent type) with persistent proteinuria and hematuria were with glomerulonephritis of various types including IgA nephropathy in 78.8% of the total cases. Therefore, proteinuria is an important sign of glomerulonephritis. In investigation in different age groups, IgA nephropathy was seen in about 40% of both pediatric and adult cases, whereas minor glomerular abnormalities and thin basement membrane disease were more frequent in pediatric cases. Tubulo-interstitial lesions and glomerular lesions in vascular or metabolic diseases were recognized more in adults than in children. Membranous glomerulonephritis (17 cases including 4 pediatric cases), complicated with malignant tumors such as bladder or rectal cancers and hepatoma was found in 3 aged patients. Examination for malignant tumor would be necessary for aged patients with membranous glomerulonephritis. As for the prognosis of IgA nephropathy, because histological changes of IgA nephropathy varied widely from very mild state to severe state, the prognosis is not always good.(ABSTRACT TRUNCATED AT 250 WORDS)