A selective medium (CFAT) was developed for the detection and enumeration of Actinomyces viscosus and Actinomyces naeslundii in dental plaque. Neutral acriflavin and potassium tellurite were used in combination with the known selective agents cadmium and fluoride to eliminate most of the competing plaque flora. Composition of CFAT per liter was as follows: Trypticase soy broth (BBL Microbiology Systems), 30 g; glucose, 5 g; agar, 15 g' cadmium sulfate, 13 mg; sodium fluoride, 85 mg; neutral acriflavin, 1.20 mg; potassium tellurite, 2.50 mg; basic fuchsin, 1.25 mg; defibrinated sheep blood, 50 ml. A. viscosus reference strains of human origin grew on CFAT without reduction in numbers under an atmosphere of 90% air-10% CO2. Animal strains of A. viscosus were inhibited at the level of cadmium in CFAT. Two of six A. naeslundii strains did not grow on CFAT. Improved recovery of A. viscosus and A. naeslundii from dental plaque occurred on CFAT, as compared with two other selective media which contained either cadmium sulfate or sodium fluoride, respectively, as selective agents. CFAT was more selective with regard to much of the extraneous gram-positive flora. Bacterionemia, Neisseria, yeasts, and streptococci were virtually eliminated.