The beneficial effect of yoghurt consumption on health and on the improvement of the mucosal immune system is well established, as is the diet-associated risk of colon cancer. In an experimental model in BALB/c mice we demonstrated that yoghurt added to the diet for 10 consecutive days, with the procedure repeated each 10 days for 6 months, inhibited the development of a colorectal carcinoma induced by 1,2 dimethylhydrazine (DMH). The immunoregulatory mechanisms involved in the inhibition of tumour growth by yoghurt were also examined in these studies. We determined B lymphocytes IgA(+) and IgG(+), as well as CD4(+) and CD8(+) T cells in the large intestine. We measured cellular apoptosis and the cytokines TNF-alpha, IFN-gamma and IL-10. An increase in the number of IgA(+) (P<0.01) was observed, but not in IgG(+) (P<0.01), or in the CD4(+) population (P<0.01) in the mice treated with DMH and yoghurt. While in the group with the carcinogen there was an enhancement in the IgG(+) B cells (P<0.01) and CD8(+) T cells (P<0.01). Yoghurt increased the number of apoptotic cells and induced IFN-gamma and TNF-alpha cytokine release, their production being regulated by an increase in IL-10 (P<0.001). We demonstrated that yoghurt may exert antitumour activity by a decrease in the inflammatory immune response mediated by IgA(+) increase, apoptosis induction and IL-10 release.