Ascites and hydrothorax from 130 patients with different diseases were examined by the AgNOR technique. The mean number of AgNOR granules per nucleus in 60 malignant ascites and hydrothorax were 4.35±2.18 and 1.80 ±0.79, respectively. The AgNORs of the former were significant higher than those of the latter (P<0.01), which suggested that this technique was useful in differential diagnosis between benign and malignant ascites and hydrothorax. Further study has shown the positive rate of AgNOR to bemuch higher (75.00%) than that through pathological examination (36.67%) (P<0.01).In addition,40 cases of exudative effusions and 20 of transudative effusions in the benign group were observed to have the mean valuesof 1.93±0.90 and 1.53 ±0.48 respectively, which indicates that this technique could also be useful in identifying exudative and transudative effusions.