In three trials, a total of 108 broiler chickens were unchallenged or challenged orally with either 10(2) or 10(6) cells of Listeria monocytogenes at 1, 14, or 35 days of age. The birds were kept in separate wire-floored brooders and growout batteries, fed unmedicated broiler-starter rations ad libitum, and killed 7 days postchallenge. The ceca, duodenum, spleen, liver (including gall bladder), and a cloacal swab were sampled from each bird and were analyzed for the presence of L. monocytogenes. In Trial 1, L. monocytogenes was recovered on all sampling days, but most frequently from birds challenged when 1 day old. In Trials 2 and 3, recovery was only from birds challenged at 1 day of age. The L. monocytogenes organism was not recovered from any uninoculated control birds. There was a dose-related colonization response (10(6) greater than 10(2]; and more recoveries were obtained from the ceca, spleen, and cloacal swabs than from the duodenum and liver.