We examined fresh urine samples from patients with hematuria using flow cytometry to evaluate its clinical usefulness and accuracy in objectively identifying glomerular and non-glomerular hematuria. Two parameter analysis was applied for forward light scattering (0LS), chiefly representing cell volume, and perpendicular light scattering (90LS), chiefly representing cell structure. In patients whose diagnosis were established by renal biopsy or diagnostic procedures, the patterns of the distribution curves of 0LS and 90LS were divided into three groups: (1) glomerular, (2) non-glomerular and (3) debris patterns. After a prospective blind study was undertaken, the results of flow cytometry were later compared with the results of clinical diagnosis. Glomerular hematuria above 30/high power field could be detected with high sensitivity (92.9%) and specificity (90.5%). Glomerular diseases showed a significantly lower peak channel number than non-glomerular diseases did (0LS: 53.8 +/- 16.4 versus 97.5 +/- 26.5, p less than 0.01, 90LS: 48.4 +/- 17.0 versus 85.5 +/- 32.9, p less than 0.01, respectively). It is suggested that flow cytometric analysis of hematuria is an useful diagnostic procedure as a rapid, non-invasive, accurate and objective test for determination of origin of hematuria.