The present study was designed to investigate the role of HLA-class I (A and B) and class II (DR and DQ) antigens and blood group phenotypes in the aetiology of inflammatory bowel disease (IBD) in a sample of Iraqi patients. The patients were also evaluated for total and differential counts of leucocytes, subpopulations of lymphocytes (CD3+, CD4+, CD8+ and CD19+ cells) and phagocytosis. Sixty-five patients with IBD were investigated during the period May-December, 2004. The disease was clinically diagnosed by the consultant medical staff at Al-kadhamyiah Teaching hospital and Gastrointestinal Tract (GIT) and liver disease Center in Baghdad. The diagnosis was based on a clinical evaluation using colonoscopy and a histopathological examination of a biopsy. According to the point view of consultants, the patients were clinically subdivided into ulcerative colitis (ULC; 50 patients) and Crohn's disease (CRD; 15 patients).