Resistance to activated protein C (APCR) has been reported with a prevalence of 30 to 40% in patients with idiopathic thrombosis. The defect responsible for APCR is a point mutation in the factor V gene (FV Leiden). The estimated frequency of FV Leiden varies from 2 to 5% in the white population with similar or lower frequency in the african american population. We undertook this study to evaluate if Factor V Leiden is a risk factor for the development of AVG thrombosis in children with ESRD. The FV Leiden mutation eliminates Mnl-1 restriction enzyme digestion site, yielding characteristic RFLP patterns for heterozygotes and homozygotes. Genomic DNA(gDNA) was extracted from peripheral blood mononuclear cells. Polymerase chain reaction (PCR) was used to amplify a 206 bp fragment of the gDNA containing the mutated site, followed by Mnl-1 digestion of the amplified product. The digests were run on 4% Nusieve agarose gels and visualized with ethidium bromide. The expected patterns were 3 bands of sizes 123, 47 and 36 bp's in patients with the normal FV gene; 4 bands of sizes 159, 123, 47, 36 bp's in heterozygotes with the Leiden mutation and 2 bands of 159 and 47 bp's in homozygotes with the Leiden mutation. We studied 19 patients(ages 6 to 22 years; median 14 years) with ESRD and AVG who were on chronic hemodialysis. 14 of these 19 patients were african american and 5 hispanic in ethnicity. The cause of ESRD was systemic lupus nephritis in 5, focal segmental glomerularsclerosis in 5, dysplastic kidneys in 3, and chronic glomerulonephritis, Bartter's syndrome, multicystic kidney disease, hypertension, Takayasu's arteritis and nephrosclerosis in one each. Six of these patients had no episodes of AVG thrombosis. Ten had 1 episode of AVG thrombosis and one of these also had thrombosis of the transplant, while three had 3 or more episodes of AVG thrombosis. Factor V Leiden was not detected in all the patients studied, irrespective of the number of thromboses, suggesting that it probably does not contribute to AVG thrombosis in children with ESRDin the study population.