Lamina propria mononuclear cells can be isolated from mucosal specimens of human colon. In the present study, we have explored whether both the phenotypes and functional properties can be studied in lamina propria mononuclear cell suspensions isolated from the same set of endoscopic biopsies in patients with ulcerative colitis. The counts of CD11b+ lamina propria mononuclear cells in mild active ulcerative colitis were significantly higher than those of both quiescent ulcerative colitis and controls. Similarly, the CD16+ and the CD19+ lamina propria mononuclear cells were significantly increased in mild ulcerative colitis patients in comparison to both quiescent ulcerative colitis and control lamina propria mononuclear cells. Lamina propria mononuclear cells from all the biopsy samples appeared to produce detectable amounts of immunoglobulins of the three classes. The production of IgG in mild ulcerative colitis cultures was significantly higher than that observed in quiescent ulcerative colitis and controls. In contrast, the production of IgA in active ulcerative colitis lamina propria mononuclear cell cultures appeared to be significantly lower than that of both quiescent ulcerative colitis and controls. This study shows that morphology, phenotypes, and functional properties can be assessed in lamina propria mononuclear cell suspensions obtained from the same set of endoscopic biopsy samples. We have also shown that changes in phenotypes and functional status of lamina propria mononuclear cells occurred in mild active ulcerative colitis while no significant abnormality of these parameters was found in quiescent ulcerative colitis. This indicates that a normalization of mucosal immune functions occurs in ulcerative colitis patients when complete clinical and histological remission is achieved.