Effect of acid of radix isatidis alkaloid ( RIAa) on adsorption and release of Newcastle disease virus ( NDV) was detected by cytopathic effect inhibition and MTT colorimetric assays. The results showed that the A570 value of RIAa at the concentration of 31. 3 μg·mL -1 when absorbed 60 min in simultaneous adding RIAa and virus after mixed was significantly higher than that of virus control ( P < 0. 05). However,the A570 values of RIAa at the three concentrations when absorbed 120 min were significantly high...