In 42 tumour samples of human neuroblastoma, histological classification by differentiation (Shimada) was significantly correlated with strong positivity for neuron-specific enolase (NSE) and inversely correlated with rosette formation. Most ganglioneuroblastomas were positive for S-100 protein and reacted strongly with NSE antibody. Histological signs of high proliferative activity included intermediate or high mitosis-karyorrhexis index, necrosis and lack of calcification, which were significantly correlated with each other. Flow cytometric DNA analysis demonstrated that 88% of the tumour samples had DNA aneuploid stem lines. High S phase fraction (greater than or equal to 0.20) was significantly correlated with necrosis and lack of calcification. Univariate analysis of prognosis for 26 patients whose tumour samples were obtained before adjuvant treatment showed that five factors were significantly related to a better outcome: early stage of the disease (stages I, II, IV-S), S phase fraction less than 0.20, favourable Shimada histology, positivity for S-100 protein, and strong positivity for NSE. In multivariate analysis, only S phase fraction or stage of disease remained significantly associated with prognosis. DNA index did not correlate with prognosis in this study.