The oral cavity is the ecological niche for Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus, but occasionally they cause severe nonoral infections. In this study we present 20 systemic or nonoral infections due to A. actinomycetemcomitans and H. aphrophilus, comprising all isolates of these species forwarded to and stored in Finnish reference laboratories during the years 1988-2000. The time from specimen collection to correct species identification was 9.3 days for A. actinomycetemcomitans and 10.7 days for H. aphrophilus. A. actinomycetemcomitans strains represented serotypes a, b, c, and d. Arbitrarily primed PCR distinguished four A. actinomycetemcomitans and six H. aphrophilus genotypes. Antimicrobial susceptibility testing with benzylpenicillin, amoxicillin, tetracycline, metronidazole, azithromycin, and trovafloxacin showed generally good activities against the present strains, and the susceptibility patterns closely resembled those of oral strains. The prolonged time to recover and identify A. actinomycetemcomitans and H. aphrophilus from systemic and nonoral infections may delay the correct diagnosis of the patient, but the good antimicrobial efficacies of antimicrobial agents against these pathogens give a good prognosis for the patients and advance the treatment of severe infections caused by these fastidious organisms of oral origin.