We evaluated the availability of toluidine blue stain in body fluids, such as peritoneal and pleural fluid and urine. Nine hundreds specimens, i.e., 400 pleural and 400 peritoneal fluids and 100 urine samples, respectively, from Jan. 1995 to May 1996 were included. We obtained the result of high sensitivity and high specificity. In toluidine blue stained body fluid in comparison with Papanicolaou stained result. Additionally, we found the diagnostically important crystals in chylothorax and some urine samples, which can not be seen in routine Papanicolaou stain. We thought the toluidine blue stain in body fluid is one of very useful diagnostic methods.