Methods for estimating glomerular volume were compared in Zenker-fixed, paraffin-embedded biopsies from 10 patients with insulin-dependent diabetes mellitus and 6 normal kidney donors. Two methods of measurement of individual glomerular volumes were used: the Cavalieri method (considered the "gold standard") and the maximal profile area (MPA) method. Also studied were the method of Weibel and Gomez and a method based on the disector principle; both estimate mean volume (VG). MPA and Cavalieri showed strong correlation (r = 0.93; P less than 0.001), although the MPA method consistently overestimated the true volume; six glomeruli were necessary for a reliable estimate of VG. The disector method did not correlate with VG determined by Cavalieri. Weibel-Gomez did correlate with Cavalieri (r = 0.68; P less than 0.05), but overestimated VG. At least 15 profiles were needed to provide a dependable estimate of VG by Weibel-Gomez. The Cavalieri, MPA, and Weibel-Gomez methods all can provide reliable estimates of VG, the latter two with appropriate correction factors. The individual glomerular volume methods, while more time consuming, provide information on variation and distribution of the glomerular population and are the methods of choice for studies of glomerular volume.