Heat-stable (HS, O-antigen) and heat-labile (HL) serotyping are the most common methods used to type Campylobacter jejuni and C. coli for epidemiologic purposes. In this study, we conducted RRNA analysis to differentiate strains of C. jejuni and C. coli that had been serotyped by use of the passive hemagglutination (heat-stable) and slide agglutination (heat-labile) methods. Ribotyping of isolates within HS and HL serotypes revealed further discrimination of strains. Four ribotypes were identified by Pvu II and Pst I digests of eight HS serotype-34 isolates. Ribotyping also differentiated strains within HL serotypes. Ribotyping also was conducted on 10 representative isolates of C. jejuni and C. coli isolated from an infant macaque. The eight ribotypes confirmed previous results of serotyping and other phenotypic analyses, which indicated that the infant was repeatedly reinfected with different strains of C. jejuni and C. coli. Results of the study indicated that ribotyping is a sensitive molecular marker for distinguishing strains of C. jejuni and C. coli. Furthermore, some isolates with similar ribotype patterns had variability in their HS and HL serotypes.