To better define the nature of intestinal T cells, the phenotypes of isolated lamina propria lymphocytes (LPL) were determined in both Crohn's disease patients and control patients using combinations of monoclonal antibodies that have been found to correlate with particular immunoregulatory functions. Isolated LPL and autologous peripheral blood lymphocytes (PBL) were stained with multiple combinations of monoclonal antibodies and studied by dual immunofluorescence flow cytometry. In LPL, compared with PBL, there was a significant increase in the proportion of T cells having the Leu-3+, Leu-8- and Leu-3+, 2H4- phenotypes (associated with helper-inducer function) and a corresponding decrease in the proportion of T cells having the Leu-3+, Leu-8+ and Leu-3+, 2H4+ phenotypes (associated with suppressor-inducer function). It was also found that in LPL, compared with PBL, the percentage of cells with the Leu-2+, Leu-15+ phenotype (associated with suppressor-effector function) was significantly lower. However, the percentage of T cells with the Leu-2+, 9.3+ phenotype (associated with cytolytic function) was similar in PBL and LPL in control patients. There were no major differences comparing Crohn's disease patients with control patients, except that the proportion of Leu-2+, 9.3+ lymphocytes was higher in PBL in Crohn's disease patients. These results show that the lymphocyte subpopulations in the lamina propria differ from those in peripheral blood in having predominantly the phenotypes of helper-inducer and cytolytic T cells, whereas the phenotypes of suppressor-inducer cells and activated suppressor cells are less frequently observed.