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Alfred Bernard, PhD, Unit of Industrial Toxicology and Occupational Medicine, Clos Chapelle-aux-Champs 30.54, B-1200 Brussels (Belgium) Dear Sir, Glycosaminoglycans (GAG) are the major constituents of the anion layer of the glomerular basement membrane which provides an electrostatic barrier to the filtration of anionic macromolecules like albumin [1]. It has been recently suggested that the increased urinary excretion of GAG observed in diabetics [2, 3] might reflect a derangement of GAG in the glomerulus, which would represent the first step toward the development of mi-croalbuminuria [4]. In support for this hypothesis, a correlation between urinary GAG and albuminuria has been reported in 25 insulin-dependent diabetics with daily excretion levels of albumin between 25 and 250 mg [5]. To assess the validity of urinary GAG as index of the charge selectivity of the glomerular basement membrane, we have compared the urinary excretion of GAG with that of albumin, retinol-binding protein (RBP; a marker of proximal tubular function), Tamm-Horsfall glycoprotein and ß-N-acetylglucosaminidase (NAG) in 69 diabetics (duration of diabetes 1–32 years, mean 13 years), in 34 workers chronically exposed to cadmium and in 15 patients with acute tubular damage due to multiple injuries, rabdomyolysis or acute poisoning. The control group consisted of 31 age-matched subjects (age 20–65 years). GAG were assayed by the method of Whiteman [6] as in the studies by Baggio et al. [4, 5]. Albumin, RBP and Tamm-Horsfall glycoprotein were measured by latex im-munoassay [7] and NAG by fluorimetry [8]. In comparison with the control group, cadmium workers, patients with acute tubular injury and diabetics exhibited an increased prevalence of elevated GAG values in urine (fig. 1: χ2 test significant for diabetics and patients with tubular injury). This prevalence parallels the mean urinary excretion of albumin, NAG and RBP, which suggests that urinary GAG might have some link with renal da6∞ (o 1,000) 500