The expression of the Fas/APO-1/CD95 receptor on the neuroblastoma cell lines IMR-32, Kelly, SK-N-SH, LS and SiMa was investigated. The induction of apoptosis was attempted by incubation with Fas antibody IgM and IgG, Fas ligand and with ceramide. All neuroblastoma cell lines proved to be positive for Fas/APO-1/CD95 receptor expression by FACS. However, propidium iodide staining in FACS showed that neither incubation with the Fas antibody nor with the Fas ligand resulted in convincing apoptosis of the neuroblastoma cells. On the other hand, incubation with ceramide rapidly led to all signs of apoptosis morphologically and in the FACS. Therefore, other pathways than Fas/Apo-1/CD95 ligation must be of significance for the apoptosis of these neuroblastoma cell lines.