A study involving 129 organic and conventional dairies in Minnesota, Wisconsin, Michigan, and New York was conducted to determine patterns of occurrence of Salmonella spp. and to identify risk factors for shedding. Visits to each farm were made at two-month intervals from August 2000 to October 2001. Fecal samples from healthy cows, calves and other targeted cattle groups and samples from bulk tank milk, milk filters, water, feed sources and pen floors were collected at each visit. Microbial culture was performed at a single laboratory. Salmonella spp.