The examination of large numbers of transitional cells in stained cytologic urine preparations failed to identify a specific cell type of renal tubular rather than transitional cell origin. The stained preparations allow a clear distinction of leukocytes from transitional epithelial cells but separation of the more degenerated epithelial cell forms from histiocytes is difficult. Epithelial cells seen in urine sediments examined as part of a routine urinalysis should be accepted as being of renal origin only when they are clearly part of casts.