The polyamines putrescine, spermidine and spermine play important roles in cell proliferation, differentiation and the modulation of ion channel receptors. However, the function of increased concentrations of these compounds in brain injury and disease is unclear since they have been proposed as being both neuroprotective and neurotoxic. The effects of spermine and putrescine were studied in human primary cerebral cortical cultures containing both neurons and glia. No toxic effects were induced at 8 days in vitro (DIV) by either of the two polyamines at concentrations ranging from 0.3 µM to 2 mM. However, when the oxidative metabolisation of spermine that generates toxic by-products was induced by the presence of foetal calf serum, spermine caused cellular death with a LC 50 of approximately 50 μM. At 14 DIV, the coapplication of spermine 2 mM and glutamate 5 mM induced neuron cell death, but the effect of applying both components separately was null. Both spermine and glutamate were toxic to older neurons (26 to 42 DIV cultures), and here the coapplication of glutamate was found always to intensify the effect of spermine. Spermine showed greater toxicity than glutamate in neurons. Another effect observed is that glutamate, but not spermine, induced astrocyte swelling. Spermine toxicity was inhibited by both MK801 and ifenprodil, indicating a mechanism involving NMDA-receptor activation. Moreover, a strong spermine modulation of the NMDA receptor was demonstrated by the inhibition of glutamate toxicity by ifenprodil. Putrescine induced minor effects also as a neurotoxic agent. In conclusion, neuronal death by spermine can be induced by its toxic by-products as well as through NMDA-receptor action. The present results confirm the potentially harmful role of the polyamines in excitotoxicity-related human disorders.