The most common cause of leukocyturia is--in conjunction with bacteriuria--an infection of the urinary tract. In the sediment, leukocytes may be differentiated into neutrophil or eosinophil granulocytes or lymphocytes. When contamination has been excluded, leukocyturia in the absence of significant bacteriuria mandates a further diagnostic evaluation. Of necessity for an accurate diagnostic work-up are appropriate urine sampling, rapid examination of the samples obtained, and standardized examination conditions.