Changes of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity in the lumbosacral intermediolateral (IML) neurons of the rat were examined for approximately 10 weeks after pelvic nerve transection. Both the number and the staining intensity of NADPH-d-positive neurons in the IML region increased remarkably 1 week after pelvic axotomy; the number of darkly NADPH-d-stained cells on the axotomized side was approximately 2.2-fold greater than on the control side. The number of NADPH-d-positive cells returned to the control level at 5 weeks and decreased significantly below the control level 10-11 weeks postaxotomy. In addition, using a retrograde tracing technique with Fluorogold (FG) combined with NADPH-d histochemistry, approximately 95% of the NADPH-d-positive IML neurons were found to send their axons to the pelvic nerve 1 week after axotomy, whereas nearly 25% of the FG-labeled neurons were found to be negative for NADPH-d. Thus, these results indicate that pelvic axotomy in the rat enhances NADPH-d activity transiently in the IML neurons of the lumbosacral spinal cord, and suggest that the IML region may include different neurons showing different responses in nitric oxide synthase expression after peripheral axotomy.