Intron 40 of the human von Willebrand factor (vWF) gene contains a polymorphic region with three variable-number tandem repeats (VNTRs), type (ATCT)(n). In the present report, we evaluated the allelic frequencies of these three VNTRs in a population constituted by 51 Brazilian Caucasian and 25 Types 1, 2, and 3 von Willebrand disease (vWD) patients, and performed segregation analysis in eight families affected by vWD Types 1 and 2. Three pairs of primers were used to amplify independently nucleotides 1640-1794 (VNTR 3), 1890-1991 (VNTR 1), and 2215-2396 (VNTR 2) from intron 40. The observed heterozygosities (0.86, 0.66, and 0.66 for VNTRs 3, 1, and 2, respectively) were in accordance with the expected heterozygosities derived from the allele frequencies (0.81, 0.64, and 0.70, respectively). Although the three VNTRs were highly polymorphic, VNTR 3 showed the highest values of heterozygosity [Haemostasis 25 (1995) 264; Hum. Mel. Genet. 1 (1992) 287.]. (C) 2000 Elsevier Science Ltd. All rights reserved.1006489494