We have previously presented evidence of a highly organized and compartmentalized structure of the small intestinal lamina propria of the pig. In this study, we conducted a detailed analysis of the T-cell populations found at this site, and compared these T cells with cell populations found in other tissue sites and the periphery. We showed that the CD4+ and CD8+ T-cell populations found in the pig gut are of memory phenotype, defined by CD45 isoform expression, but show few signs of recent activation. They show a high degree of phenotypic and therefore presumably functional homogeneity. Both CD4- and CD8-positive cells show strong parallels in the patterns of surface molecule expression, suggesting similar pressures on differentiation. The unique combination of surface molecules found on lamina propria T cells is found only infrequently on cells in other lymphoid sites.