Muscle tissue obtained by needle biopsy from 20 diabetic subjects and from 20 age-matched control subjects was divided into two portions, one of which was fixed and processed by our routine procedure (primary glutaraldehyde fixation followed by osmium fixation and embedment in araldite) and the other was fixed initially in osmium tetroxide and embedded in maraglas, the procedure employed by Siperstein et al. Basement-membrane width of capillaries was measured by the 20-point method of Siperstein et al. and by the two-minimum-point technic developed in our own laboratory. Contrary to the experience of Siperstein et al., the prevalence of basement-membrane thickening in diabetic subjects based on mean width values and/or standard deviations in excess of 95 per cent tolerance intervals was highest (65 per cent) in minimum measurements of glutaraldehyde-fixed tissues and lowest (30 per cent) in osmium-fixed tissues (X2 = 4.9123, p less than 0.05). Internal discrepancies in the data of Siperstein et al. indicate that (1) their basement-membrane-width values derived from multiple measurements from control subjects are anomalous (low) and (2) the very high prevalence of basement-membrane thickening they reported in diabetic and in prediabetic subjects and considered as strong support for their conclusion that basement-membrane disease is independent of and precedes glucose intolerance is suspect.