Apoptosis is the selective physiologic deletion of cells that are no longer required. Over-expression of the bcl-2 proto-oncogene extends survival of neurons otherwise destined for apoptosis. The unique capacity of neuroblastoma (NB) to undergo spontaneous regression and the prognostic dichotomy of children with this malignancy led us to evaluate bcl-2 expression and apoptosis in NB. An in situ DNA nick-labeling technique to detect apoptotic cells, as well as immunohistochemistry and morphology, were utilized in a selection of NB tumor specimens and in the human fetal sympathetic nervous system. bcl-2 expression was present in all 28 NB tumors examined and in sympathetic ganglia of the human fetus. Measurement of overall bcl-2 expression and of extent of apoptosis correlated with favorable prognosis. In low-stage tumors, bcl-2 expression was most intense in poorly differentiated tumor cells adjacent to fibrovascular stroma. Cells distant from the stroma exhibited increasing degrees of chromaffin differentiation, with apoptosis most evident in bcl-2-negative neuroblasts adjacent to well-differentiated NB cells. The spatial distribution of bcl-2 expression, apoptosis and chromaffin differentiation in favorable-prognosis NB may provide insight into mechanisms of persistent tumor existence or regression.