Lactic acid fermentation is the simplest and safest way of preserving food and has probably always been used by humans. Species such as Lactobacillus plantarum, Lactobacillus rhamnosus, Lactobacillus paracasei, Lactobacillus acidophilus, and Lactobacillus salivarius are common in the human mucosa, from the mouth to the rectum. In food, L. paracasei and L. rhamnosus are usually associated with dairy products whereas L. plantarum is found in fermented foods of plant origin. A probiotic food product containing no milk constituent was launched in Sweden in 1994. The product is a lactic acid fermented oatmeal gruel that is mixed in a fruit drink. It contains approximately 5 x 10(10) colony-forming units of L. plantarum 299v/L. The strain L. plantarum 299v originates from the human intestinal mucosa and has been shown in rats to decrease translocation, improve mucosal status, improve liver status, improve the immunologic status of the mucosa, and reduce mucosal inflammation. In humans, L. plantarum 299v can increase the concentration of carboxylic acids in feces and decrease abdominal bloating in patients with irritable bowel disease. It can also decrease fibrinogen concentrations in blood. Should probiotics be administrated through foods, the probiotic organism must remain vigorous in the food until consumption and the food must remain palatable, ie, the food carrier and the organism must suit each other. L. plantarum 299v not only affects the bacterial flora of the intestinal mucosa but may also regulate the host's immunologic defense. The mechanisms involved need to be clarified.