The intestinal contents of 3,090 broilers, one day to five weeks of age, from 1,025 broiler houses, were examined for the presence of Listeria monocytogenes. L. monocytogenes was isolated in 243 cases, i.e. 23.7% of the broiler houses, 58.8% were of type 1, 35.5% of type 4b, 1.2% were of type 5 and 2.4% of the strains could not be typed. In spite of cleaning and disinfection after the chickens had been taken to the poultry slaughterhouse, reinfection occurred in the broiler houses in 16.9% of the cases; this occurred as many as eight times in succession. Various serotypes were isolated on one farm. Listeria organisms in the intestinal contents of healthy broilers do not affect the growth rate. Contaminated deep-litter (chips of white deal-wood) is a potential danger for man and animals, especially when used inn loose-housings on cattle farms.