BACKGROUND Nephropathy has long been recognized as a potential complication of congenital cyanotic heart disease (CCHD). The present study was undertaken to investigate some aspects of glomerular function by measuring urinary total protein, microalbumin, and tubular function by assessing urinary alpha-1-microglobulin. The structural integrity of the renal proximal tubules was also studied by measuring urinary activities of the brush-border enzyme leucine-aminopeptidase and the lysosomal enzyme -acetyl-beta-d-glucosaminidase. The levels of hematocrit (Hct) and oxygen saturation were also investigated as predisposing factors for renal impairment in CCHD. METHODS These investigations were done by recruiting 86 children who were grouped as follows: the control group (G1 ) consisted of 14 children (aged 4-12 years); the other 72 children with CCHD were divided according to age (ie, duration of cyanosis) into 4 equal groups, each containing 18 patients: G2 (age <1 year), G3 (age > or = 1 year and <5 years), G4 (age > or = 5 years and <10 years), and G5 (age > or = 10 years). In addition, 10 of the 72 patients underwent a palliative surgery and were included as G6 (regardless of age: 2 from G3, 4 from G4, and 4 from G5 ) to study the effect of the palliative surgery on the above-mentioned parameters. RESULTS Results of the present work showed that with increasing duration of cyanosis (ie, on going from G2 to G5 ) among the studied children with CCHD, there was a significant elevation in the urinary excretion of the investigated functional and structural parameters of the glomeruli and proximal tubules compared with the control children. The data also showed a significant increase in Hct, whereas oxygen saturation was significantly decreased. Results of G6 after the palliative surgery demonstrated a significant decrease in the urinary excretion of the investigated parameters of the kidney, with a significant decrease in Hct and increase in oxygen saturation levels, compared with the results of the patients of this group before the palliative surgery. CONCLUSIONS These results suggest impairment of both glomerular and tubular functions as well as structure of the proximal tubules among children with CCHD and that the palliative surgery has significantly improved this impairment.