A study of the significance of lymphocytic infiltration was made in a retrospective series of 23 primary neuroblastomata. The degree of lymphocytic infiltration was estimated and scored in 5 categories. Non-parametric rank order statistical methods were used to establish quantitative correlations, particularly with the duration of survival. A significant positive correlation was found both in infancy and childhood. It was found, unexpectedly, that the presence of metastases did not invalidate the correlation between lymphocyte score and survival.