Quantitative determinations of beta2-microglobulins were carried out in 335 urinary samples collected from 335 subjects living in villages with a high rate of morbidity and mortality from endemic Balkan nephropathy. Three months after the first determination of beta2-microglobulin excretion, blood and urine samples were obtained from 19 patients with high values and from 19 with normal values of beta2-microglobulins. The results of the biochemical and immunological investigations performed on these samples suggest that the tubular alteration is the first lesion. The autoimmune phenomena elicited by the tubular alteration may contribute, by an antigen-antibody complex disease mechanism, to the appearance of glomerular secondary lesions.