PURPOSE:To investigate the relationship between the proliferative activity of refinoblastoma (RB)cell and the RB differentiation degree and the infiltration capability. METHOD:The proliferating cell nuclear antigen (PCNA)expression in RB tissues of 48 cases was analysed by using LSAB immunohistochemical method. RESULTS :The mean PCNA labelling index(LI)in differentiated RB tissues of 12 cases was markedly lower than that in non-differentiated of 36 cases(P＜0.05). The mean PCNA LI in RB tissues of the optic nerve infiltrated group(22 cases)was significantly higher than that of the optic nerve non-infiltrated group(26 cases)(P＜0.05). The results indicate that the PCNA LI is significantly related with the differentiation degree of RB and the infiltration capability. CONCLUSION :The determination of PCNA LI is of significance for evaluating the histologic characteristics and biological behavior of RB.