The nucleotide (nt) sequence of the Helicobacter pylori (Hp) napA gene, encoding neutrophil-activating protein A (HPNAP) was determined. Alignment of this sequence with those of known bacterioferritins (Bfr) revealed sequence homology and conservation of a 7-amino-acid (aa) motif constituting the ferroxidase (Frx) center of Bfr in the HPNAP. The N-terminal aa sequence deduced from the iron-regulated mrgC gene of Bacillus subtilis [Chen et al., J. Bacteriol. 175 (1993) 5428–5437] is highly similar to that of HPNAP and contains five Frx center aa residues. The deduced aa sequences for proteins of unknown function in Treponema pallidum [Walfield et al., Infect. Immun. 57 (1989) 633–635] and in the cyanobacterium Anabaena variabilis [Sato, GenBank accession No. JU0384 (1991)] identify these two proteins as Bfr. Although the DNA-binding protein from starved cells of Escherichia coli [Almiron et al., Genes Dev. 6 (1992) 2646–2654] is clearly a HPNAP/Bfr homologue, a significant part of its Frx center is missing. It is unlikely that the intracellular function of HPNAP is related to its ability to activate neutrophils.