From 1981 to 1987, renal specimens obtained from 91 children with idiopathic nephrotic syndrome were categorized into 5 histologic subgroups, according to the WHO classification. We analyzed differences in the ratios of the size of the mesangial stalks and attached capillary, including the Bowman's space between the capillary tufts (E), mesangial matrix (Mx), and approximate capillary lumens (E-Mx) to the whole glomerular area of these subgroups using the histomorphometer-IBAS. Focal segmental glomerulosclerosis with diffuse mesangial proliferation (FSGS + DP) had the largest matrix area (Mx/G > 0.5), and smallest capillary lumen size (E/G-Mx/G) (0.3474 +/- 0.0702). On the contrary, FSGS with minimal change (FSGS + MC) had the smallest mesangial matrix (Mx/G), 0.2834 +/- 0.07726, but preserved a larger capillary lumen (0.427 +/- 0.1215). The approximate size of capillary lumens, from the smallest to the largest, was in the following order: FSGS + DP, diffuse mesangial proliferative glomerulonephritis (DPGN), focal segmental proliferative glomerulonephritis (FSPGN), FSGS + MC and minimal change nephrotic syndrome (MCNS). The ratio of the total number of mesangial cells to the area of the whole glomerulus (MCN/G) derived from the light microscopic examination was parallel to the value of Mx/G obtained by the histomorphometric technique. In summary, we introduced the histomorphometric technique using the histomorphometer-IBAS for quantitative measurement of various areas in the glomeruli. The data derived from the system is compatible with those obtained by experienced nephrologists, suggesting that the histomorphometric technique is helpful in histopathology. It is hoped that this new methodology will be used more extensively in the near future.