The potential of Salmonella contamination in hatching cabinets to 1) generate seeder chicks and 2) interfere with the efficacy of competitive exclusion (CE) treatments was investigated in six experiments. Hatchery-generated seeder: chicks were produced by hatching in the same hatcher with inoculated eggs (immersed in a 1.0 x 10(5) cfu/mL suspension of Salmonella typhimurium or inoculated with 10(5) to 10(6) cells on the air cell membrane). Salmonella spread through the hatching cabinet to chicks hatching from uninoculated eggs in adjacent trays. In two experiments, Salmonella was isolated from 31 and 100% of the chick rinses after the birds were held in groups for 3 d in isolation units. When these hatchery-generated seeder chicks were stocked in floor pens at a 1:10 ratio with uncontaminated contact chicks, the pen environment became contaminated to the extent that greater than 50% of the contact chicks became contaminated. In two experiments with only one to three inoculated eggs per 200 egg hatching cabinet, 98% of uninoculated chicks were intestinally colonized with Salmonella after the birds were held 1 wk in isolation cabinets. This hatchery-acquired Salmonella substantially reduced the effectiveness of subsequent CE treatments to prevent Salmonella colonization of the young chicks. These studies demonstrate that control of Salmonella in hatching cabinets is critically important for control of Salmonella in broilers.