The study was carried out in an attempt to explain the familial character of endemic Balkan nephropathy and of agglomeration of cases in certain households and in the ascendency of certain families. The hypotheses of a genetic disease or that of an infectious etiology have been taken into consideration in previous studies - by chromosomal analyses and statistical-mathematic tests of contagiousness - without being able to find arguments in support of one or the other hypotheses. This study brings important elements in favour of the possible role of ecologic factors and mainly of the hydrictoxic one, in the determination of the familial agglomerations in endemic nephropathy. Thus using radionuclear determination methods, we could demonstrate in a locality of the endemic area that around the water sources with high content of nephrotoxic oligoelements (cadmium, chromium, manganese, cobalt) there are more diseased families than around water sources poorer in these oligoelements.