Fimbrial-associated protein, an attachment factor of Actinobacillus actinomycetemcomitans, was genetically analysed by cloning. The plasmid obtained was found to harbor a 1.7kb fragment which contained a 228bp open reading frame encoding 76 amino acids (7.970kDa). The fimbriae associated protein gene (fap) was strongly expressed in fimbriated A. actinomycetemcomitans 310a but not in non-fimbriated strains. (C) 1997 Academic Press Limited.