Abstract Thirty-three specimens of dental calculus were examined for species of Actinomyces, Arachnia, Rothia and Bacterionema using the fluorescent antibody (FA) technique. Each specimen contained 2–4 species of Actinomyces with A. israelii being present in 99 per cent of the specimens but A. bovis was not found in any specimen. When all 9 Actinomycetaceae species were considered, the number of species per sample ranged from 3 to 7. The total Actinomycetaceae count had a mean of 1·9 × 107 organisms per gram wet weight, while the total microscopic count had a mean of 8·9 × 1010 organisms per gram wet weight. The FA technique rapidly and specifically identifies species of Actinomycetaceae in dental material, and with further improvement will be applicable for the enumeration of these organisms.