Technical Abstract: Mature lactating dairy cattle were sampled on four farms, all located within a five-mile radius, in August 2001, January 2002 and again in August 2002. Fecal samples were collected via rectal palpation and cultured for E. coli O157:H7 and Salmonella. A portion of the Salmonella isolates were serotyped and examined for genetic relatedness using pulsed field gel electrophoresis. Fecal shedding of E. coli O157:H7 and Salmonella varied considerably between farms and at the different sampling times. Large fluctuations in the percentage of positive animals were observed from summer to summer for both of these pathogens. Similarly, Salmonella serotype and serotype prevalence varied from farm to farm and within farm from one sampling time to another. Multiple Salmonella genotypes were detected for a number of serotypes and identical genotypes were found on different farms with one genotype of Salmonella Senftenberg identified on three of the four farms. This study demonstrated the wide variability in pathogen shedding within and among dairy farms all located in a small geographical region and highlights the complexity of pathogen control at the farm level.