Growth retardation is a common manifestation of chronic renal failure in children. To gain insight into the alterations of bone growth plate of chronic uremia, a morphometric study of tibia proximal growth plate was performed in 5/6 nephrectomized rats (NX, n = 4) and sham animals (SHAM, n = 4). Toluidine blue stained sagittal sections (5-6 microns) from ethanol-fixed and methylmethacrylate-embedded tibias were analyzed. Widths (X +/- SEM) of growth plate (GPW), proliferative (PZW) and hypertrophic zones (HZW) were calculated. Results were as follows: [table: see text] Growth plate modifications in uremia are rather due to alterations in the hypertrophic than proliferative zone. This is consistent with an abnormal metabolism of condrocytes as shown by a lower mean area of extracellular matrix (EMA) per cell in the hypertrophic zone of the NX rats (0.23 vs. 0.58 microns 2).