Two group Ia muscle spindle afferents were impaled in the lumbosacral enlargement of the cat's spinal cord and intra-axonally labeled with horseradish peroxidase. Terminations in lamina VI were examined with the electron microscope. Boutons formed synaptic associations with somata and large dendritic shafts in the lamina VI neuropile and received axo-axonic contacts. It is concluded that group Ia terminals synapse with the proximal regions of lamina VI neurons and are under strong presynaptic control.