The results of low molecular weight (LMW) proteinuria test in urines of patients and suspect subjects in an endemic area of Balkan endemic nephropathy (BEN) in Yugoslavia are reported. An accordance between the positive LMW test and the clinical diagnosis of BEN has been found in more than 70%. The authors claim that LMW immunodiffusion test is a very useful procedure for detecting BEN and a great aid in the epidemiological work in the endemic field. The results of determining beta2-microglobuline (beta2m) in serums and urines by radioimmunoassay technique as well as counting of clearances of endogenous creatinine in healthy persons, "endangered" subjects in endemic area, and BEN patients without azotemia, with azotemia and uremia are reported. The group of 17 patients suffering of BEN without azotemia having slightly or more markedly lowered creatinine clearances showed higher serum and much higher urinary concentration of beta2m which are not in proportion with creatinine clearance. The results are interpreted so far as a consequence of the predominant tubular lesion in BEN. In groups of patients with azotemia and uremia no differences in beta2m handling have been found. The report has a preliminary character and requires further study.