PURPOSE: We have used a novel leukocyte adhesiveness/aggregation test (LAAT) to show that many patients with inflammatory bowel disease (IBD) in clinical remission have a subclinical low grade inflammation. METHODS: Included in the study are 500 controls, 96 patients with IBD in remission, and 106 patients in relapse. RESULTS: The percent of aggregated white blood cells detected in the peripheral blood was 5.9 +/- 3.9, 9.1 +/- 5.9, and 18.8 +/- 9.4, respectively. The difference between each group and any other was significant at P < 0.0001. Similar results were obtained when other acute phase reactants like the erythrocyte sedimentation rate, white blood cell count, differential count, and C-reactive protein level were examined. However, in a linear regression analysis, LAAT was the only significant (P < 0.0006) variable that could classify correctly each subject to the appropriate category of control and IBD in remission or relapse. CONCLUSIONS: Identification of patients with IBD in clinical remission who have ongoing inflammation may be of clinical-therapeutic relevance. The LAAT is a simple, rapid, and convenient test. The present study indicates that it is also very sensitive.