A Salmonella agona strain has caused a hospital outbreak of gastroenteritis in a pediatric unit in Rio de Janeiro. It bears two plasmids, a small (6·5 MDa molecular weight) plasmid coding for type B colicin production and a larger one (36 MDa molecular weight) determining resistance to ampicillin, gentamicin, kanamycin and trimethoprim-sulphamethoxazole. The R-plasmid, but not the Col-plasmid, is self-transferable to a Escherichia coli recipient strain. Curing for the R-plasmid was achieved by treatment with 0·05 % SDS followed by incubation at 44°C. It has not been possible to cure the S. agona strain for its Col-plasmid.