Twenty-seven compounds were screened for their ability to sensitize Streptococcus sanguis to killing by light from a 7.3-mW Helium/Neon (HeNe) laser. Bacteria were mixed with various concentrations of the test compounds, spread over the surfaces of agar plates, and then exposed to light from the HeNe laser for various time periods. The plates were then incubated and examined for zones of inhibition. Those compounds found to be effective photosensitizers were then tested against Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Fusobacterium nucleatum. Toluidine blue O, azure B chloride, and methylene blue at concentrations of 0.005% (wt/vol) were effective photosensitizers of all four species, enabling killing of bacteria following exposure to laser light for only 30 s.