From October 1993 to August 1994, broiler chickens in four grow-out houses, two previously used (houses 1 and 2) and two newly constructed (houses 3 and 4), were used in a study to determine the source, time of infection, and prevalence of Campylobacter spp. Cecal droppings and cecal samples were obtained from the broilers. Samples were also obtained from water, feed, litter, soil, fans, and workers' boots. Samples were obtained from domestic animals and wildlife species (rectal swabs), including insects, on or near the premises. Broilers in houses 2, 3, and 4 became infected in the second or third week and were fully colonized by day 42. Campylobacter appeared in house 1 during week 2 in a low percentage of the birds, disappearing by the fourth week. Isolates were also recovered from domestic pigs and water on this farm. In house 3, the organism was isolated from workers' boots and a wild bird prior to isolation from the broilers. Following isolation from cecal droppings, the organism was isolated from water, feed, litter, feathers, flies, cattle, feces, and wild animals. In house 2, Campylobacter was isolated from cattle feces and wild birds prior to week 5, when the broilers first became infected, and thereafter from water, feed, insect, and wildlife, and cecal droppings. It was subsequently isolated from workers' boots, cattle feces, feathers, insects, and other wildlife. All ceca taken from 20 birds each from houses 2 and 3 were positive at time of slaughter (day 49). All ceca from house 1 were negative. No ceca were collected from birds originating in house 4. No specific source could be identified from the samples obtained, although apparently the organism permeates the environment and several potential sources are discussed in this paper.