Despite the opinion of many scientists and laymen that lactobacilli benefit adult intestinal health, the medical and scientific communities do not accept this as fact. This paper offers possible beneficial and detrimental roles which lactobacilli could play; relevant literature citations also are made. Healthful roles include those exerted as a result of their presence as members of the intestinal flora as well as their benefits as culture or enzyme preparations. Speculative detrimental effects discussed are nutrient competition, carcinogen activation and detoxification interference (glucuronide hydrolysis).