Recovery of the suggested probiotic strain Lactobacillus GG in feces was studied after oral administration. Lactobacillus GG was given to 20 healthy human volunteers for 7 days in gelatine capsules with daily doses of 1.6 x 10(8) cfu and 1.2 x 10(10) cfu. All the volunteers in the higher dose group had detectable numbers of Lactobacillus GG in their feces during the test period. The strain was detected in feces of all the volunteers after 3 days of administration. No effect was observed on the total number of fecal lactobacilli. Fecal detection of the strain may facilitate dose-response studies and provide a useful tool in dietary studies utilizing the strain in foods or food-type products.