The closely related species Actinobacillus actinomycetemcomitans Haemophilus aphrophilus, and Haemophilus paraphrophilus are common findings in oral microbiota, The aims of this study Here to evaluate the applicability of the Rapid NH and API ZYM kits and arbitrarily primed PCR IAP-PCR in the identification and differentiation of the three species from each other, The material included 62 clinical isolates and three reference strains of A. actinomycetemcomitans representing the 5 serotypes and 18 AP-PCR genotypes. Haemophilus species included 12 clinical isolates and 11 reference strains of II. aphrophilus, Ii, paraphrophilus, and 5 other species. For the PCR amplification, the oligonucleotide 5'-CAGCACCCAC-3': was used as a primer, Contrary to the consistent performance of API ZYM, the Rapid NH system was able to identify only 10 of 65 (15%) A. actinomycetemcomitans isolates, whereas all Haemophilus species Here correctly identified. The API ZYM test differentiated A. actinomycetemcomitans from Ii aphrophilus and Ii. paraphrophilus by negative beta-galactosidase and alpha-glucosidase reactions and a positive esterase lipase reaction, However, the API ZYM test was unable to differentiate Ii aphrophilus from H. paraphrophilus, it also could not differentiate A.,. actinomycetemcomitans serotypes from each other. Among the Ii. aphrophilus isolates three AP-PCR genotypes and among ii. paraphrophilus isolates only one AP-PCR genotype, distinct From those of A. actinomycetemcomitans, . H-ere found. The Rapid NH test showed poor ability to identify clinical isolates of all A. actinomycetemcomitans serotypes, Moreover, AP-PCR genotyping proved to be a rapid method for the species differentiation of A. actinomycetemcomitans. ii. aphrophilus, and H. paraphrophilus.