The long term goal of this study is to treat and/or prevent periodontal-diseases in humans by means of laser radiation directed specifically toward black-pigmented Bacteroides, the strongly implicated causative agent. This unique approach is possible, because laser radiation can be selectively toxic to black-pigmented Bacteroides: these bacteria possess endogenous porphyrins, which absorb laser radiation, transmitting that energy to acceptors, rendering them toxic. The major, tangible objective of this proposal is to determine in vitro conditions which will best facilitate damage to selected species of black-pigmented Bacteroides exposed to Argon dye laser radiation. The effect of laser radiation will be assessed as a function of radiation wavelength, radiation dosage, and bacterial cell concentration, both in growth and non-growth environments. Also examined will be the influence during laser exposure of exogenous photosensitizing agents, molecular oxygen concentration, and bacterial species other than black-pigmented Bacteroides. This project should disclose experimentation designed to determine if laser radiation has a deleterious effect on the black-pigmented Bacteroides. When the project is completed, an answer can be given to the question: "Does laser radiation offer the dental profession a practical and safe means of selectively destroying species of black-pigmented Bacteroides, thereby preventing and/or treating forms of destructive periodontal disease?" Should the answer to this question be affirmative, the results of this investigation will be extremely valuable for subsequent evaluation of the selective toxicity of laser radiation against the black-pigmented Bacteroides, first using experimental animal systems, ultimately in periodontally diseased humans.