Desferrioxamine (DFO) has shown anti-proliferative and cytotoxic effects on several tumor cells. DFO is used at present in the treatment of neuroblastoma in combination with chemotherapy (D-CECaT regimen: cyclophosphamide, etoposide, carboplatin, and thiotepa). We compared the effect of continuous or intermittent exposures to DFO on 3H-thymidine uptake, viability, and cell cycle of human neuroblastoma (NB) cell lines. Our results show that continuous exposures to DFO cause dose- and time-dependent cytotoxicity of NB cells, while intermittent exposures result in significant NB cell toxicity only when using high DFO concentrations. By 3H-thymidine uptake, a significant inhibition of proliferation was observed only in continuous exposures. In addition, a consistent arrest in G1 phase was detected only in cultures treated continuously with high DFO concentrations. Our data indicate that 3H-thymidine uptake, viability, and cell cycle changes are proportional to the extent of exposure and concentration of DFO, suggesting that in vivo DFO continuous infusion may improve anti-neuroblastoma activity.