The School Health Law of Japan was passed in 1974 mandating urine screening of elementary and junior high-school students for the detection of renal disease. A first morning urine was obtained on an annual basis for each individual student for the time period 1974-1986. The prevalence of proteinuria and haematuria among elementary school children was 0.08% and 0.54%, respectively, while junior high-school students demonstrated corresponding prevalences of 0.37% and 0.94%. The theoretical merits of this screening programme include the detection of glomerulonephritis with possible early therapeutic intervention. However, a limitation to this approach is its over-sensitivity where asymptomatic urine abnormalities is found to be 10 times greater in frequency than glomerulonephritis histologically.