Many immunological abnormalities have been described in inflammatory bowel diseases (IBD). Even though, no clear cut primary defects have yet been described, some therapeutic trials have targeted either immunocompetent cells or overproduction of cytokines. Preliminary results have shown that antisense oligonucleotides (anti-ICAM), anti-cytokine antibodies (anti-TNF) or recombinant human cytokines (IL-10 or IL-11) are effective in some patients with Crohn's disease refractory to steroids. However, these data need to be confirmed and the potential side effects of these treatments must be further considered. These drugs need to be more precisely defined in particular compared to corticotherapy. Finally, data from immunomodulation strategies should help us understand the aetiology of abnormal immune responses in Crohn's disease (CD) and ulcerative colitis (UC).