The small intestinal villus epithelium in day-old pigs was replaced in 7-10 days, while that in 3-week-old pigs was replaced in 2-4 days. Decreased replacement time with age was associated with an increase in crypt depth and a decrease in villus length. Epithelia in the large intestine were also replaced more slowly in day-old than in 3-week-old pigs. Squamous epithelia in esophagus and stomach were replaced at similar rates in both age groups.