Neuronal mortality, interleukin-1 beta (IL1 beta) and tumor necrosis factor-alpha (TNF alpha) release were measured in hypoxic hippocampal neuronal cultures. Release of IL 1 beta and TNF alpha was already observed in normoxic cultures, but after hypoxia it was increased approximately 2-fold. Pretreatment with 2-amino-5-phosphonovaleric acid (APV), the N-methyl-D-aspartate (NMDA) receptor antagonist, not only decreased neuronal mortality as expected, but also dramatically lowered cytokine release. However, there was no relationship between the neuronal mortality and the release of each cytokine both in untreated hypoxic cultures and in APV-pretreated ones. We conclude that IL 1 beta and TNF alpha release in hypoxia are dependent on the activation of the NMDA receptor, but that this is not the main mechanism of hypoxia damage in in vitro neuronal cultures.