During a period from January to June, 1966, a severe outbreak of bovine salmonellosis occurred in Manitoba. The disease was diagnosed clinically in approximately 50 herds. Salmonella organisms were isolated from carcasses or specimens on 24 different farms involving approximately 2,379 cattle the most frequently isolated serotype was S. newport (92 per cent). The source of infection was traced to bonemeal and mineral supplements. The bonemeal and one of the mineral mixtures originated at one local feed mill. Out of 20 bonemeal samples collected at the affected farms during or shortly after outbreaks occurred, 19 yielded Salmonella organisms, most of which contained more than one serotype. Cultures of three mineral samples were also positive for Salmonellae. The serotypes isolated from cattle corresponded with those isolated from unused portions of bonemeal or mineral on 16 premises... Salmonella organisms (including S. newport) were isolated from bonemeal samples at retail outlets, bags stored at the feed mill and the environment of the mill. Bones used for the production of the bonemeal and other animal by-products used as feed ingredients were collected from two rendering plants which supplied the feedmill and these were positive for Salmonellae. There was a 100 per cent increase in 1966 in the incidence of human infections with S. newport in Manitoba compared to the previous year... Stricter sanitary conditions in rendering plants and feed mills could prevent similar recurrences of contamination of animal feeds with Salmonellae. This in turn would reduce the risk of infection in animals and man.