Evaluation of antimicrobial agents is based on in vivo and in vitro studies. The minimum inhibitory concentrations (MICs) of sodium benzoate and dichlorobenzyl alcohol to 115 strains of plaque microorganisms were determined by a broth-dilution method. Sodium benzoate did not inhibit growth of any gram-positive cocci (MIC > 106,590 microM). MICs for Porphyromonas gingivalis and two strains of Treponema socranskii were 26,650 microM. The MIC of dichlorobenzyl alcohol to the reference strain of Actinobacillus actinomycetemcomitans was 723 microM and to P. gingivalis, two strains of T. socranskii, and Candida albicans 1,446 microM. MICs for other organisms were 2,892 to 5,784 microM. Saliva samples from 10 volunteers, collected at various times after toothbrushing with a dentifrice containing 10% sodium benzoate and 0.3% dichlorobenzyl alcohol, were analyzed gas-chromatographically. Immediately after toothbrushing mean levels of sodium benzoate and dichlorobenzyl alcohol were 372,626 microM and 7,529 microM, respectively. After 5 min mean levels were 38,700 microM and 734 microM. In conclusion, the concentrations of both antimicrobials dropped rapidly during the first 30 min, but for 5-10 min they were high enough to inhibit growth of potential periodontal pathogens.