Rectal swabs or faecal samples from 992 domestic animals and 97 human patients in the Nairobi region were cultured for thermophilic Campylobacter species and Yersinia enterocolitica. The highest isolation rate of campylobacters was obtained from diarrhoeic pigs (55.1%), followed by healthy chicken (51.5%), diarrhoeic dogs (47.2%), healthy pigs (44.0%), healthy ducks (29.4%), healthy goats (6.3%), healthy cattle (5.8%), diarrhoeic humans (3.1%), and healthy sheep (2.0%). Only one strain of Y. enterocolitica was obtained. This isolate, which conformed to Nilehn's biotype 1, was recovered from one (0.7%) of the 150 healthy pigs examined. Out of 317 thermophilic campylobacters isolated, 163 (51.4%) were classified as C. jejuni, whereas 127 (40.1%) belonged to C. coli. The remaining 27 strains fell into three categories which did not conform to any defined species. Of the total number of isolates, 74.1% were resistant to metronidazole, 90.9% were resistant to triphenyltetrazolium chloride (TTC), and 50.2% reduced selenite. The results indicate that domestic animals may play a significant role in the epidemiology of human campylobacteriosis in the Nairobi region by serving as reservoirs. Y. enterocolitica seems to be rare among man and animals in this area.