Elevated plasma fibrinogen levels have been identified as an independent risk factor for coronary heart diseases, stroke and peripheral artery disease. The -455G/A polymorphism in the promoter region of the beta-fibrinogen gene has been associated with increased plasma fibrinogen levels. However, the functional effect of this polymorphism has been controversial and other polymorphisms in the fibrinogen gene have also been implicated in higher fibrinogen levels. In this study, we evaluated the transcriptional activity of 4 natural haplotypes and 6 artificial haplotypes in the promoter region of the beta-fibrinogen gene. Significantly lower IL-6-induced activity was observed in the -1420A and -148T alleles. In contrast, the -854A allele had significantly higher activity. Artificial haplotypes containing the -1420A, -854A and -148T alleles were also analyzed to confirm individual functional effects. The -1420A and -148T alleles significantly lowered the activities, while the -854A allele significantly raised the activity. From this study we conclude that the -1420G/A, -854G/A and -148C/T polymorphisms in the beta-fibrinogen promoter region are functional polymorphisms while the -455G/A polymorphism may not be a functional one, and that the association of the -455G/A polymorphism with higher fibrinogen levels may actually be due to linkage disequilibrium between the -455G/A polymorphism and other truly functional polymorphisms.