This study compared the ability of a nonradioactive digoxigenin-labeled DNA probe and anaerobic culture to identify subgingival Porphyromonas gingivalis. Total cellular DNA from P. gingivalis ATCC 33277T was labeled using the Genius kit from Boehringer Mannheim Biochemicals. Anaerobic culture was performed using VMGA III transport medium and enriched brucella blood agar. The DNA probe could detect as little as 1000 P. gingivalis cells added to supragingival plaque. Also, the probe could detect P. gingivalis when it was present in proportions too low to be visualized on overgrown bacterial plates. The probe showed no visible reaction with strains of various oral species or with thousands of non-P. gingivalis colonies from plaque samples. VMGA III could maintain the viability of P. gingivalis for up to 6 days, as evidenced by DNA probing of colony blot of subgingival cultures. A total cellular DNA probe for detecting P. gingivalis seems to offer a simple and reliable method of detecting the organism in subgingival specimens.