In order to better define changes in the relative proportion of peripheral blood T-lymphocyte subpopulations in patients with inflammatory diseases of the bowel, we performed simultaneous three-color fluorescence-activated cytometric (FACS) analysis using fluorophore-conjugated monoclonal antibodies with specificity for CD4, CD8, Leu 8, and CD45RA on 22 normal control subjects, 28 patients with Crohn's disease (CD), 15 patients with ulcerative colitis (UC), and 11 patients with intestinal inflammation secondary to etiologies other than inflammatory bowel disease (NIBD). This staining combination allowed enumeration of distinct T-cell subpopulations as follows: virgin CD4+, recall antigen helper T cells, nonspecific B-cell helper T cell, virgin CD8+, cytotoxic effector and suppressor effector and recall antigen cytotoxic T cells based on a synthesis of published functional analyses. No differences in the proportion of CD4+ or CD8+ cells or in the CD4+/CD8+ ratios were evident when UC and NIBD patients were compared to normal subjects. A significant reduction in the proportion of CD4+ cells and an increase in CD8+ cells was observed, however, in the CD group. When two-color analysis was performed, several significant differences in the proportions of circulating lymphocytes were seen. Specifically, these included significant increases in the number of CD4+, Leu 8- (P < 0.01) cells in all disease groups and an increase in CD4+, CD45RA+ cells in the NIBD group. Conversely, significant decreases in the proportions of CD8+, Leu 8+ (P < 0.01) cells were evident in the Crohn's disease group.(ABSTRACT TRUNCATED AT 250 WORDS)