A molecular typing approach for Campylobacter jejuni and Campylobacter coli was developed with restriction fragment length polymorphism analysis of a 9.6-kb PCR-amplified portion of the lipopolysaccharide gene cluster. Sixty-one Penner serotype reference strains were analyzed with this new genotyping scheme, and 32 genogroups were found. Eleven additional genogroups were obtained from 87 clinical C. jejuni strains tested. This molecular typing method shows a correlation with the Penner heat-stable serotyping method, a phenotypic typing method based on lipopolysaccharide structures that is often used as a "gold standard" for subtyping Campylobacter spp. This strong correlation suggests that the data obtained can be directly compared with epidemiological data collected in the past by classical serotyping of C. jejuni and C. coli. In contrast to the high percentage of nontypeability by phenotyping, this molecular typing method results in 100% typeability and provides a superior alternative to serotyping.