The sixth, seventh and eighth exons of both alleles of the C1-inhibitor gene were nucleotide sequenced in 52 individuals from 20 kindred with type I hereditary angio-oedema (HAE), 5 kindred with type II HAE and 10 control kindred. Four previously unreported nucleotide which had no disease specificity were identified in addition to a sequencing error in the eighth exon. In addition, a T → C mutation at position 8770 (resulting in a Phe → Leu substitution at position 291) was identified on the abnormal allele of the affected members of a family with type I HAE due to an exon 6 donor splice site mutation. The significance of this mutation is not known. Disease-specific mutations were identified in 100% of type II HAE kindred and in 20% of type I HAE kindred. The relevance of these findings to the evolving understanding of the molecular genetics of HAE is discus