Ras p21 expression was investigated in 28 cases of neuroblastomas and 12 cases of ganglio-neuroblastomas by the biotin-streptavidin immunoperoxidase method using the anti-ras p21 rat monoclonal antibody Y13-259. The results showed that 28% of neuroblastomas and 92% of ganglio-neuroblastomas demonstrated elevated ras p21 expression. However, in this series of patients 10 of 12 ganglio-neuroblastomas were staged as early disease (stage I or II) compared to 15 of 28 neuroblastomas, with similar staged disease. On analysing all of these tumours into early and late disease (i.e. stage I and II; and stage III and IV) a correlation was found between p21-ras overexpression and early disease (P<0.0001). As staging of neuroblastomas has been considered to be a prognostic indicator, it is argued that ras p21 over-expression maybe an indicator for a favourable prognosis in these patients.