We investigated the prevalence of two reported mutations of the factor V gene (factor V Arg(306) --> Thr, or factor V Cambridge, and factor V Arg(306) --> Gly) in 104 relatively young patients with verified venous thrombosis and in 208 age-, sex- and race-matched controls, in order to establish whether the two mutations are associated with increased predisposition for venous thrombosis. PCR amplification followed by BstNI and MspI digestion was employed to determine the genotypes, and each mutation was confirmed by DNA sequencing. Among the controls, one individual was found to be heterozygous for the factor V Arg(306) --> Thr mutation and one heterozygous for the factor V Arg(306) --> Gly mutation: none of the patients carried either mutation, Our findings do not support factor V Cambridge and factor V Arg(306) --> Gly as risk factors for venous thrombosis.