The neurophysiological basis of low back pain (LBP) is poorly understood. Low back muscles are considered a possible source of LBP. This study was undertaken to find and investigate the responses of spinal dorsal horn neurones receiving input from low back muscles. The recording of the dorsal horn neurones was performed at the spinal segment L3 because pilot experiments had revealed that afferent fibres from the erector spinae muscle beside the spinous process L5 mainly originate in the dorsal root ganglion L3. Two neurones out of 38 had receptive fields in deep low back tissues (one in muscle) in non-treated control animals. When the animals were given injections of nerve growth factor (NGF, 0.8 mM, 2 x 25 ml) into the erector spinae muscle one day prior to the recording, the number of neurones that had a receptive field in the low back was significantly increased (9/38 neurones, p < 0.05, Fisher's exact probability test). The results suggest that the processing of the input from low back muscles is shifted two segments rostrally relative to the location of the muscles, and that the dorsal horn neurones can be sensitised to mechanical stimuli by NGF.