Brain-derived neurotrophic factor (BDNF) can produce hyperalgesia in the adult rat. Here we assessed whether changes in the spinal release of the nociceptive peptide substance P (SP) contributes to this effect. Antibody-coated microprobes revealed a significant basal release of SP in the dorsal hornin vivothat was increased following acute knee inflammation. Microinjection of BDNF into the grey matter (0.5 μl, 10−5M) altered SP release neither in rats with normal knees nor in rats with inflamed knee joints. In the lumbar dorsal horn slice preparation in vitro, superfusion with BDNF (100 ng/ml) could reduce SP release evoked by electrical dorsal root stimulation without modyfing SP basal outflow. It is unlikely, therefore, that enhanced spinal SP release mediates the hyperalgesic effect of BDNF.