Lactic acid bacteria are present in many foods such as yoghurt and are frequently used as probiotics to improve some biological functions of the host. Many researchers have evaluated the effects of yoghurt and lactic acid bacteria against diseases such as cancer and intestinal inflammation. The preventive effect of probiotics on intestinal carcinogenesis may be associated with changes in the intestinal microbiota, suppressing the growth of bacteria that convert procarcinogens into carcinogens. Other mechanisms could be related to the immune response modulation and have been evaluated using milks fermented with lactic acid bacteria in chemically induced colon cancer and hormone-dependent breast cancer models. We demonstrated, using a murine colon cancer model, that yoghurt consumption inhibited tumour growth by decreasing the inflammatory response by increasing IL-10-secreting cells, cellular apoptosis and diminishing procarcinogenic enzymes. Milk fermented with Lactobacillus helveticus R389 delayed breast tumour growth by decreasing IL-6 and increasing IL-10 in serum and in the mammary glands and tumour-infiltrating immune cells. Previous results obtained with yoghurt administration in a colon cancer model led us to analyse its effect on a trinitrobenzenesulfonic acid-induced intestinal inflammation model in mice. Yoghurt was able to attenuate the symptoms of acute inflammation by reducing inflammatory cytokines, and increasing regulatory cytokine IL-10-producing cells, leading to desirable changes of the intestinal microbiota. It was demonstrated, by using murine models, that the consumption of fermented milks can modulate the immune system and can maintain it in a state of surveillance, which could affront different pathologies such as cancer and intestinal inflammation.