They review 49 studies about effects of probiotic bacteria on human health. 26 of the studies concerned the prevention or treatment of diarrhoea, 9 the prevention of cancer or formation of carcinogens, 7 the decrease of cholesterol levels, and 7 with the stimulating effects on the immune system. The bacteria involved in these studies were Lactobacillus GG (22), Lactobacillus acidophilus (16), Bifidobacterium bifidum (6), and Enterococcus faecium (7). Evidence for the prevention of bacterial o viral diarrhoea was not strong, except for the shortening of diarrhoea by rotavirus infection by Lactobacillus GG. The other effects were inconsistent. They conclude that more placebo-controlled studies are needed to determine the effects of probiotics on human health.