Abstract The effect of blocking nerve conduction on retrograde horseradish peroxidase (HRP) labeling was investigated for rat hindlimb motoneurons. Conduction of the sciatic nerve in the left leg was blocked with tetrodotoxin, and HRP solution was injected into the medial gastrocnemius (MG) muscles of both sides. The total number of labeled MG motoneurons and the labeling intensities of individual cell somas were measured. There were no differences in these two parameters between the blocked and the intact sides. The results suggest that motoneurons are sufficiently well labeled with HRP, even if they are electrically silent.