The nucleotide sequences of the genes encoding the subunits of Klebsiella pneumoniae and Salmonella typhimurium type 1 fimbriae were determined. Comparison of the predicted amino acid sequences of the two subunits revealed domains in which the sequences were highly conserved. Both gene products possessed signal peptides, a fact consistent with the transport of the fimbrial subunit across the membrane, but these regions showed no amino acid homology between the two proteins. The predicted N-terminal amino acid sequences of the processed fimbrial subunits were in good agreement with those obtained by purification of the fimbrial subunits.