A pure culture of potentially pathogenic bacteria was obtained from 90% of 233 joints examined, originating from 232 ducks condemned due to arthritis at slaughter. S. typhi-murium and Staph. aureus were isolated from 61% and 18% of the joints respectively. E. coli was obtained from 6% of the cases, serogroup 078 being most prevalent. E. rhusiopathiae, Y. pseudo-tuberculosis, P. vulgaris, Micrococcus sp., Streptococcus sp., Acinetobacter sp., Flavobacterium sp., Pseudomonas sp. and Ae. formicans made up 12 cases. Serotypes other than S. typhi-murium were prevalent among ducks from all farms investigated, but S. typhi-murium was the only serotype demonstrated in arthritis. A high incidence of S. typhi-murium in the intestinal tract of ducks maintained on free range or in open houses suggests that these sites are sources of infection and that the intestinal tract is the portal of entry for S. typhi-murium causing arthritis. Ducks with arthritis at slaughter should always be totally condemned because of the public health hazard from the organisms most often associated with this condition.