Strong experimental evidence implicates the corticospinal tract in voluntary control of the contralateral forelimb. Its potential role in controlling the ipsilateral forelimb is less well understood, although anatomical projections to ipsilateral spinal circuits are identified. We investigated inputs to motoneurons innervating hand and forearm muscles from the ipsilateral corticospinal tract using multiple methods. Intracellular recordings were made from 62 motoneurons in three anaesthetized macaque monkeys. Monkeys were deeply anesthetised with sevoflurane (3-5% in 100% O2) and alfentanil (7-23 µg kg-1 h-1 by IV infusion) during a laminectomy for exposure of spinal segments C6-T1. The anesthetic regime was then switched to an intravenous infusion of propofol (5-14 mg kg-1 h-1) and alfentanil (doses as above). Neuromuscular blockade was achieved by infusion of atracurium (0.6-1.2 mg kg-1 h-1). Continuously monitored vital signs included heart rate, arterial and venous blood pressure, blood oxygen saturation, end-tidal CO2, and core temperature. Depth of anaesthesia was verified by ensuring that there were no changes in heart rate or arterial blood pressure in response to peripheral nerve stimulation). No monosynaptic post-synaptic potentials were observed following single and multiple shock stimulation of the ipsilateral corticospinal tract (300μA, Fig. 1). Single stimulus intracortical microstimulation of the primary motor cortex (M1) in two awake behaving monkeys (up to 30μA) failed to produce any responses in ipsilateral muscles. Strong stimulation (>500μA, single shock) of the majority of corticospinal axons at the medullary pyramids revealed only weak suppressions in ipsilateral muscles at longer latencies than the robust facilitations seen contralaterally (Fig. 2). Spike triggered averaging of ipsilateral muscle activity from M1 neural discharge (184 cells) did not reveal any post-spike effects consistent with monosynaptic corticomotoneuronal connections. We conclude that, in normal adults, any inputs to forelimb motoneurons from the ipsilateral corticospinal tract are likely to be weak and indirect.