The rate of human intestinal infections with more than a single Campylobacter strain was determined and the genetic variabilities of Campylobacter strains throughout an infection episode were investigated by means of pulsed-field gel electrophoresis (PFGE) and enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR). For 48 and 49 of 50 patients, all isolates from one sample showed identical patterns by PFGE and ERIC-PCR, respectively. Throughout an infection episode in 47 of 52 patients, the PFGE fingerprints of the isolates remained stable, while in 1 patient two different species were observed and in 4 patients different patterns were observed. Therefore, ERIC-PCR proved less discriminative than PFGE. These findings suggest that human infection with more than one Campylobacter strain is rare and should not significantly impair epidemiologic analyses. However, changes in the genetic fingerprint throughout an infection should be considered in the assessment of epidemiologic studies of Campylobacter spp.