Five hundred strains of thermophilic Campylobacter spp. from sporadic cases of enteritis and from epidemiologically related infections connected with outbreaks were serotyped. The haemagglutination method of Penner and the slide agglutination method of Lior were used together. Greater discrimination was obtained by the use of two methods together than by either alone; 96% of sporadic strains were typed using a restricted set of typing sera. Of the sporadic strains, 50% fell within five Penner serotypes and 50% fell within four Lior serotypes, so the increased discrimination obtained by using both methods was particularly useful amongst these most common serotypes. In outbreaks associated with one serotype both methods gave consistent results, and in outbreaks due to multiple serotypes the two methods complimented each other.