ABSTRACT This study explores a new approach for antimicrobial therapy with light activation of targeted poly- l -lysine (pL)–chlorin e6 (c e6 ) conjugates. The goal was to test the hypothesis that these conjugates between pL and c e6 would efficiently target photodestruction towards gram-positive ( Actinomyces viscosus ) and gram-negative ( Porphyromonas gingivalis ) oral species while sparing an oral epithelial cell line (HCPC-1). Conjugates of c e6 with pL (average molecular weight, 2,000) having a positive, neutral, or negative charge were prepared. Illumination with red light (λ max = 671 nm) from a diode array produced a dose-dependent loss of CFU from the bacteria, under conditions that did not affect the viability of the epithelial cells. For P. gingivalis , the cationic conjugate produced 99% killing, while the neutral conjugate killed 91% and the anionic conjugate killed 76% after 1 min of incubation and exposure to red light for 10 min. For A. viscosus , the cationic conjugate produced >99.99% killing while HCPC-1 cells remained intact. The importance of the positive charge was shown by the effectiveness of c e6 -monoethylenediamine monoamide (a monocationic derivative of c e6 ) in killing both bacteria. The clinically employed benzoporphyrin derivative under the same conditions killed epithelial cells while leaving P. gingivalis relatively unharmed. A mixture of c e6 with pL did not show phototoxicity comparable with that of the cationic conjugate. These results were explained by the selective uptake of the conjugates by bacteria (20- to 100-fold) compared to that by mammalian cells, while free c e6 showed much less selectivity for bacteria (5- to 20-fold). The data suggest that the cationic pL-c e6 conjugate may have an application for the photodynamic therapy of periodontal disease.