Campylobacters isolated from mussels and oysters in The Netherlands were analysed by a novel assay, based on DNA amplification with primers, based on semiconserved GTP-binding sites of a putative GTPase gene. Polymerase chain reaction (PCR) was followed by a single step reverse hybridization line probe assay (PCR-LiPA). This permits identification of Campylobacter jejuni, C. coli, C. lari and C. upsaliensis. Among a group of 44 isolates, three C. jejuni, one C. upsaliensis, one double infection with C. jejuni and C. coli, and 38 C. lari strains were identified. These results were in complete agreement with conventional identification methods and whole cell protein analysis. One C. hyointestinalis isolate was not identified by the PCR-LiPA, since the reverse hybridization assay does not comprise specific probes for this particular species. PCR products from 36 C. lari isolates were sequenced and phylogenetic analysis revealed the presence of two major C. lari subgroups: one comprised 11 highly homologous sequences, whereas the 25 sequences in the other subgroup were more heterogeneous. This confirmed earlier findings that C. lari isolates comprise a more heterogeneous group of isolates as compared with C. jejuni, C. coli and C. upsaliensis. Based on the sequence information, a novel PCR-LiPA was developed that permits specific and rapid detection of the different C. lari variants.