1. Glomerular sialic acid was chemically measured in rats with experimental proteinuria induced by N,N'-diacetylbenzidine (DAB) or with autoimmune Heymann nephritis.
2. In DAB nephrosis and in Heymann nephritis the relative amount of glomerular protein was increased. In DAB nephrosis the quantity of sialic acid expressed per amount of protein was decreased, but expressed per amount of DNA, which reflects the number of cells, there was no significant change. In Heymann nephritis the amount of sialic acid was not significantly altered when expressed per amount of protein or per amount of DNA.
3. In individual animals, the amount of glomerular sialic acid expressed per amount of protein or per amount of DNA did not correlate with the severity of proteinuria. An increase in the total number of glomerular cells was found only in Heymann nephritis.
4. The results suggest that proteinuria in the reported models is not the result of changes in glomerular sialic acid.