Hyperhomocysteinemia is well documented in chronic renal failure (CRF) and premature and progressive occlusive vascular disease is common in CRF. The combined effects of renal failure, folate and vitamin B(12) levels, and a common mutation (C677T) in the methylenetetrahydrofolate reductase (MTHFR) gene that leads to total plasma homocysteine (tHcy) elevation in CRF children were investigated. Forty-two children (15 females) with CRF, mean age 10.3+/-4.7 years, were included. The mean glomerular filtration rate (GFR) was 37.3+/-16.9 ml/min per 1.73 m(2). The control group comprised 33 children (18 females) with a mean age of 8.6+/-3.4 years. There were 40% of CRF patients with hyperhomocysteinemia. Folate and vitamin B(12) deficiencies were identified in 14% (n=6) and 5% (n=2), respectively, of all patients. On univariate analysis, the tHcy serum concentration was negatively correlated with the plasma folate concentration (P<0.05) in controls, and with GFR (P<0.05) in patients. On multiple regression analysis for the predictors of tHcy serum concentrations, folic and vitamin B(12 )were significant in controls, whereas only GFR was significant in CRF children. In our patients no effect of the MTHFR polymorphism on tHcy levels was seen This result, in addition to the limited number of patients, may partially be explained by the low prevalence of folate deficiency in our patients.