Five unrelated subjects with dysfunctional coagulation factor VII (FVII) were studied in order to identify missense mutations affecting function. Exons 2 to 8 and the intron-exon junctions of their FVII genes were amplified from peripheral white blood cell DNA by PCR and screened by SSCP analysis. DNA fragments showing aberrant mobility were sequenced. The following mutations were identified: in case 1 (FVII:C < 1%, FVII:Ag 18%) a heterozygous A to G transition at nucleotide 8915 in exon 6 results in the amino acid substitution Lys-137 to Glu near the C-terminus of the FVIIa light chain; in case 2 (FVII:C 7%, FVII:Ag 47%) a heterozygous A to G transition at nucleotide 7834 in exon 5 results in the substitution of Gln-100 by Arg in the second EGF-like domain; in case 3 (FVII:C 20%, FVII:Ag 76%) a homozygous G to A transition at nucleotide position 6055 in exon 4 was detected resulting in substitution of Arg-79 by Gln in the first EGF-like domain; in case 5 (FVII:C 10%, FVII:Ag 52%) a heterozygous C to T transition at nucleotide position 6054 in exon 4 also results in the substitution of Arg79, but in this case it is replaced by Trp; case 4 (FVII:C < 1%, FVII:Ag 100%) was homozygous for a previously reported mutation (G to A) at nucleotide position 10715 in exon 8, substituting Gln for Arg at position 304 in the protease domain. Cases 1, 2 and 5 evidently have additional undetected mutations.