A new commercial serotyping set based on heat-stable Penner's antigens was compared with pulsed-field gel electrophoresis (PFGE) with SmaI and SacII restriction endonucleases. Among 50 isolates of Campylobacter jejuni from Finnish patients, which represented predominant PFGE patterns selected from isolates from sporadic cases and isolates associated with small outbreaks, 11 different serotypes were demonstrated from 43 typable isolates. Several PFGE patterns could be found within one serotype; on the other hand, several serotypes could be demonstrated within one PFGE type. Most isolates originated from sporadic cases; however, some isolates were epidemiologically associated and showed identical serotypes and PFGE patterns. Although the new serotyping set would have been useful in the few epidemic cases studied, several isolates (14%) representing the major PFGE patterns remained untypable or gave weakly positive agglutination reactions only suggesting a plausible serotype (18%). This might restrict the use of the novel serotyping set, at least in Finland.