Manure-borne bacteria can be transported in runoff as free cells, cells attached to soil particles, and cells attached to manure particles. The objectives of this work were to compare the attachment of fecal coliforms (FC) to different soils and soil fractions and to assess the effect of bovine manure on FC attachment to soil and soil fractions. Three sand fractions of different sizes, the silt fraction, and the clay fraction of loam and sandy clay loam soils were separated and used along with soil samples in batch attachment experiments with water-FC suspensions and water-manure-FC suspensions. In the absence of manure colloids, bacterial attachment to soil, silt, and clay particles was much higher than the attachment to sand particles having no organic coating. The attachment to the coated sand particles was similar to the attachment to silt and clay. Manure colloids in suspensions decreased bacterial attachment to soils, clay and silt fractions, and coated sand fractions, but did not decrease the attachment to sand fractions without the coating. The low attachment of bacteria to silt and clay particles in the presence of manure colloids may cause predominantly free-cell transport of manure-borne FC in runoff.Manure is the primary source of pollution from animal feeding operations. There are an estimated 376,000 livestock operations in the United States, which generate 58.1 million tons of manure each year. According to the 1998 National Water Quality Inventory, approximately 60% of the pollution in rivers and 45% in lakes come from agricultural sources (12). Animal feces are deposited on land by grazing animals, and livestock manure and wastes from processing facilities are increasingly applied on agricultural soils in the form of solid or liquid slurries as fertilizers for silage, grazing, or crop production. Livestock manures/wastes may contain pathogenic bacteria, such as Listeria monocytogenes, Campylobacter spp., Salmonella spp., and certain strains of Escherichia coli, which may be released into the environment in large numbers (20,27,35,43,45). Sixty-five outbreaks of human infections linked to water have been reported in the United Kingdom in 1991 to 2000 (22), while 230 outbreaks have been reported in the United States in 1991 to 1998 (7).The transport of manure-borne pathogenic organisms in overland flow may be a significant cause of surface water contamination (6,11,25,40). Numerous experimental studies indicate that overland flow can transport substantial amounts of fecal bacteria on steep pastoral land (4, 11, 41), grazed pastures (11, 40, 43), or grassland and crops receiving cattle slurry (21, 34). Curriero et al. (8) have reported statistically significant correlations between the increase in heavy rainfall events and waterborne disease outbreaks in the United States for the period 1948 to 1994.It is generally recognized that bacteria in runoff can be transported as free cells or cells attached to soil particles, to fragments of vegetation and residue, and to manure particles (14,23,33,44). R...