There is a lack of uniformity in the methods of quantitative estimation of leukocytes in the urine, and considerable difference of opinion prevails concerning the normal number of these cellular elements. Pflaumer,1 Hill,2 Dyson,3 Dingwall-Fordyce4 and Amberg5 agree that normal urine, that is, urine of healthy children, may contain pus cells, but they do not offer any opinion as to what constitutes a normal maximum. Helmholz6 believes that the uncentrifugalized urine of boys should contain not more than 2 or 3 cells per low-power field, and that of girls not more than from 6 to 8. For some time, we have been interested in this matter and have felt that the number of leukocytes in the urine has diagnostic and prognostic value.7 The present study is an attempt to define normal and pathologic urine of children in terms of the cell content per