We had the opportunity of studying an epidemic of autochthonous amoebiasis occurring in the autumn of 1974 in a small town of 4000 inhabitants 30 km from Grenoble. Attention was originally attracted by the occurrence in this town of two cases of hepatic amoebiasis and one of intestinal amoebiasis identified by rectoscopy. Systematic investigations (coproctic examinations and serological tests for amoebiasis by indirect antibody fluorescence) were then carried out on everyone in the locality with digestive disorders which were possibly referable to amoebiasis, and on the other members of their families. A total number of 148 coproctic examinations were made and in two cases revealed the presence of vegetative forms of Entamoeba histolytica. In both cases the infestation provoked few symptoms (asthenia, vague abdominal discomfort, intermittent and apparently banal diarrhoea). On the other hand 20 out of 94 serological tests revealed positive results, 14 of which were equal to or greater than a titre of 1/100, a level at which all risks of non-specificity are virtually ruled out under our experimental conditions. Material reasons made it impossible to subject these cases to repeated faecal checks, but in two of them at least the rectoscopic appearances were very suggestive of subacute intestinal amoebiasis. Moreover, amoebic disease appears to be well confirmed by the results obtained among the patients as a whole by treatment with Metroinidazole. A variety of hypotheses on the origin of this epidemic have been put forward and then abandoned (market garden produce, receipt by certain families of exotic frut from overseas). In actual fact water seems to be the point of departure, for, although specimens of water taken at 7 different levels in the water supply system failed to reveal the presence of a single amoeba, bacteriological analyses during autumn 1974 showed signs of faecal contamination. The locality, which is situated at the foot of the Chartreuse massif, receives its water solely from springs but there is a holiday camp for the staff of an international airline situated above the main water catchment.