Porphyromonas gingivalis is associated strongly with severe periodontitis, but little information is available on possible transmission routes of this species. This study evaluated three DNA-based molecular typing methods for use in epidemiological surveys of P. gingivalis. In total, 32 isolates from eight married couples were investigated by: (i) restriction endonuclease analysis (REA) of whole chromosomal DNA; (ii) hybridisation of DNA fragments with ribosomal DNA (ribotyping); and (iii) amplification of DNA by the polymerase chain reaction with arbitrary primers (AP-PCR). The data obtained with the three methods were in broad agreement: in six of the eight couples, the isolates from husband and wife were indistinguishable, but isolates from unrelated individuals showed distinct types with all three methods. For some isolates, minor differences in REA pattern were obtained which could not be correlated with differences in ribotype or AP-PCR type. Ribotyping showed differences between isolates from one individual, which were indistinguishable with the other two methods. The patterns obtained with ribotyping or AP-PCR were simple in comparison to the relatively complex REA patterns. Although all three methods were concordant, AP-PCR was found to be the least time-consuming method. The data support the suggestion that P. gingivalis can be transmitted between spouses.