Fecal samples from 545 diarrheic lambs on 12 ranches in southern Idaho and western Montana were examined for potential enteric pathogens. On 3 of the 12 ranches, enterotoxigenic Escherichia coli, Salmonella typhimurium, or S dublin was implicated as the etiologic agent. Rotavirus and coronavirus were identified on 1 ranch and rotavirus alone on another. Salmonella arizonae serotype 26:30 was isolated from the feces of diarrheic lambs on 6 of the 12 ranches in this study. Pregnant ewes from 1 of the 6 ranches in which S arizonae was enzootic were transported to the Montana Veterinary Research Laboratory and studies on S arizonae were conducted in lambs from these ewes. Salmonella arizonae was shown to elaborate an enterotoxin, the activity of which was reduced when assayed in the gut loop test, using lambs from ewes vaccinated with an S arizonae 26:30 bacterin. Oral challenge inoculation of 22 young colostrum-fed lambs with S arizonae 26:30 failed to produce any significant enteric disease, in contrast to oral challenge inoculation with S. oranienburg which resulted in death, with severe diarrhea and dehydration, in 4 of 6 lambs tested. Salmonella arizonae serotype 26:30 appears to be well adapted to the ovine host and may not be a significant cause of diarrheal disease on ranches where it is enzootic.