Objective To analyse the effect of BHK21 cell on result for plaque assay in detection of Japanese encephalitis vaccine,live,and reduce the error in the detection system. Methods To test the effect of the cell growth status of BHK21 cell on the stability of the detection system by comparing different passage frequency under different concentrations of BHK21 cell. Results The better growth cells were obtained with good shape,smooth edge,transparent cytoplasm,uniform distribution,and more than 95% viability,wh...