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Stool samples from a total of 1,008 persons were examined for intestinal parasites during a comprehensive study on the epidemiology of small fluke infections in Laos. The prevalence of small fluke eggs in the stool was seen to peak at age 20 years, particularly in men from villages (90.4%). Three quarters of infections belong to the category of light infections and only 0.6% to the category of very heavy according to eggs per gram of feces (EPG). The highest EPG was in the 11-15 year age group. In addition, the following parasites were diagnosed: Sarcocystis hominis (prevalence more than 10% in the group over 20 years of age), Taenia sp. (12.4% for the village people over 20 years), Fasciolopsts buski (3.8% for the same group). The habit of Laos people to eat raw fish, beef and pork flesh, is reflected in significant epidemiological consequences. Cercariae of Opisthorchis viverrini occurred in 0.5% of Bithynia siamensis goniomphalus examined, Haplorchis sp. cercariae were found in 0.9% of Tarebia granifera snails. Metacercariae of O. viverrini were found in flesh of 7 species of cyprinid fish. Haplorchis taichui in 4 species of these fish, and H. pumilio of two cyprinid species. Hampala macrolepidota harbored larvae of all above mentioned species. Stellantchasmus falcatus was recovered in fins of belonid fish Xenentodon cancila. Adults of O. viverrini were found in 36% of domestic and stray cats, Heterophyid flukes were found in 24% cats. The most frequent species were H. taichui and H. yokogawai. Eight Laotian students were treated in Czechoslovakia with praziquantel to determine fluke infection. Three were infected only by O. viverrini, four only by H. taichui and one by both O. viverrini and H. taichui. These results demonstrate the problem of correct differential diagnosis of food-borne small fluke infections and the need to assess the clinical course and public health aspects of infections.