The production of the plasmid-encoded fimbrial antigen CFA/I of enterotoxigenic Escherichia coli requires two DNA regions: CFA/I region 1 and CFA/I region 2. These two regions are separated by about 40 kb on the wildtype plasmid. CFA/I region 1 contains the structural genes, whereas CFA/I region 2 contains a positive regulator. The first two genes (cfaA and cfaB) and the cfaD' sequence of region 1 have already been described. Here the total nucleotide sequence of region 1 is presented. Two new genes in region 1 are described, named cfaC and cfaE. The GC content of the genes in region 1 is 33.6% which is substantially lower than normally found in E. coli genes (50%). The codon usage also differs from the standard codons used in E. coli.