Determination of sialidase activity in hepatocellular carcinoma（HCC） to complete the mechanism study of GD3 change in HCC.A sensitive assay for ganglioside sialidase activity was used based on the specific binding of ricinus communis agglutinin II（RCAII） to lactose reside. The substrate used for sialidase assay was ganglioside GM3 coated on a 96-well microtiterplate. After removing sialic acids from the terminal positions of the ganglioside glycans by sialidase

the glycans were subjected to biotin-labeled RCAll. Then

the ABC assay was used to deter-mine the activity of sialidase. The activities of sialidase with both soluble form and membrane-bound form in HCC decreased significantly as compared with those in peritumor tissue. Our results indicated that the increase in gan-glioside GD3 in HCC is not only due to the enhancement of GD3 sythase activity but also due to the decrease in the sialidase activity.