The prevalence of 18 selected bacterial species was assessed by means of "checkerboard" DNA-DNA hybridisation in a group of 12 Saudi-Arabian adolescents with Papillon-Lefèvre syndrome. A total of 36 tooth sites were investigated. The patients exhibited severe periodontal disease with deep pockets. All 12 patients harboured the putative bacterial pathogens P. intermedia, F. nucleatum, P. micros and S. intermedius while T. denticola, B. forsythus, P. nigrescens, E. corrodens, S. noxia and C. rectus were recovered from 11 patients. P. gingivalis was recovered from 9 patients and 18 sites while corresponding figures for A. actinomycetemcomitans were 8 and 19, respectively. A number of the investigated species (B. forsythus, T. denticola, P. intermedia, C rectus) reached high levels (> or =10(6) cells) in more than 1/2 of the patients. On the other hand, bacteria such as A. actinomycetemcomitans and P. gingivalis were infrequently encountered at high levels in these subgingival samples. In conclusion, the analysis failed to demonstrate a PLS-specific profile of the subgingival infection, since the bacterial composition of the sampled sites closely resembled that characterising deep pockets in adult periodontitis patients.