A G-to-T point mutation in exon 2 of the FXIII A-subunit gene results in a leucine rather than valine at amino acid position 34 of the factor XIII molecule. The presence of leucine has been associated with a reduced risk of both arterial and venous thrombosis. We examined the prevalence of this point mutation in 102 cases of pre-eclampsia and 208 matched control subjects, as inherited and acquired risk factors for arterial and venous thrombosis are associated with an increased risk of pre-eclampsia. The GT genotype was observed in 38% of controls and 29.4% of cases and the TT genotype was observed in 6.7% of controls and 5.9% of cases. In subjects heterozygous for the T genotype (GT) the relative risk of pre-eclampsia was 0.7 [95% confidence interval (CI95 ) 0.4-1.1] when compared with the GG genotype. For subjects homozygous for the T allele the relative risk for pre-eclampsia was 0.8 (CI95 0.3-2.1) when compared with the GG genotype. The risk associated with the T allele in the heterozygous and homozygous forms compared with the GG genotype was 0.7 (CI95 0.4-1.1). We conclude that the presence of leucine at this site is not associated with a protection against pre-eclampsia to the magnitude of that reported in other thrombotic disease.