Forty-seven Penner heat-stable (HS) serotype reference strains for Campylobacter jejuni and 47 serologically non-typable strains were examined by pulsed field gel electrophoresis (PFGE) DNA restriction analysis. The SmaI and KpnI digest profiles were compared by numerical analysis. Most strains grouped differently in the two analyses but strain lineages were inferred where the two agreed. Genetic relationships between reference strains in the cross-reacting HS4 complex were examined. Three clonal lines were evident and comprised: (i) HS4, HS13 and HS16; (ii) HS50 and HS65; (iii) HS43. The majority of those C. jejuni expressing HS antigens not recognised by currently available antisera had > 50% PFGE DNA digest similarity to one or more Penner scheme reference strain(s) and so did not necessarily represent distinct genetic lineages. PFGE analysis provided a high level of discrimination amongst strains of C. jejuni but overall similarity estimates for defining types must be based on the analysis of more than one restriction pattern.