Ninety four strains of Listeria monocytogenes of different serovars and phagovars as well as of varying origins were characterized by ribosomal RNA gene restriction polymorphism. After digestion by EcoRI or HindIII, chromosomal DNAs were hybridized with a cloned rDNA probe from Bacillus subtilis that included the 16S rRNA gene. The 94 strains were divided into 14 ribovars according to the different hybridization patterns generated by cleavage with EcoRI. Less important genomic heterogeneity could be detected when DNAs were digested by HindIII. EcoRI ribovars analysis allowed to describe a new typing scheme which did not corroborate routine typings such as serotyping and phage typing. It also confirmed a new view of this species in exhibiting a clone gathering most human strains, as first inferred from multilocus enzyme analysis (Piffaretti et al., 22).