The exbB and exbD genes of Haemophilus influenzae (Hi) were cloned and sequenced. The deduced Hi ExbB and ExbD proteins possessed 27 and 28% amino-acid identity (56 and 58% relatedness) with the Escherichia coli ExbB and ExbD proteins, respectively; two proteins which function as TonB accessory proteins during biopolymer transport. Plasmid-encoded Hi exbB and exbD partially complemented an E. coli exbB/exbD mutation.