We developed and evaluated a PCR-based-restriction endonuclease analysis method to detect and analyze the tonB gene of Haemophilus influenzae and Haemophilus parainfluenzae from pediatric patients undergoing tonsillectomy and adenoidectomy. Multiple sites from the same patient, including the surface of adenoids and tonsils, as well as the core of tonsils, were cultured on chocolate agar and identified using standard procedures and the API NH Kit. A total of 55 H. influenzae isolates were recovered from different sites of 20 patients, and 32 H. parainfluenzae isolates were recovered from various sites of 12 patients. DNA was extracted from American Type Culture Collection strains and test isolates by the PureGene kit. Two primers, G1 (21-mer) and G2 (23-mer), were designed by us to amplify by PCR the tonB gene that consists of an 813-bp fragment. A nested PCR using primers T1 (23-mer) and T2 (24-mer) that flank an internal sequence to the gene of the order of 257 bp and restriction endonuclease digestion using XhoI and BglII were done to detect whether heterogeneity within the gene exists between the two species. Reverse transcription-PCR (RT-PCR) was finally done to detect transcription of the gene in both species. Our data have shown that the tonB gene was detected in both species. It is known to encode a virulent protein, TonB, in H. influenzae; however, demonstration of its presence in H. parainfluenzae is novel. Nested-PCR and restriction endonuclease analysis have shown that the tonB gene is apparently structurally the same in both species, with possible differences that may exist in certain H. parainfluenzae isolates. RT-PCR done on selected numbers of H. influenzae and H. parainfluenzae have shown that the tonB gene was transcribed in both species. This shows that the TonB protein, if expressed, may play a different role in the virulence in H. parainfluenzae since it is not needed for heme or heme complexes uptake as with H. influenzae.