A Gel exclusion chromatographic method was used to determine the molecular weight distribution, and therefore, the origin, of non-dialysable urinary glucoconjugates in normal men. The results showed a mixture of glucoconjugates with molecular weight ranges of 1605 to 141,000. It is suggested that the high molecular weight forms originally constitute the glucoconjugates, and that they are probably post-glomerular in origin. These may be degraded in vivo by glucosylhydrolases to produce the low molecular weight forms. The activities of the urinary enzymes may be reduced in male type 1 diabetic patients, and this may be responsible for the reported increase in their excretion of non-dialysable urinary glucoconjugates.