Some stroke patients show a balance disturbance. To know the nature of the balance disturbance, we measured the involuntary responses during standing, the long latency response (LLR), which is known as a kind of transcortical reflex. The subjects included 5 stroke hemiplegics with spasticity and 5 healthy control subjects. LLR is evoked by sudden toe-up perturbations around the ankle joint (8 degrees, 20 degrees per second). Two types of perturbation method were employed, both bilateral and unilateral. Electromyographic responses in bilateral anterior tibial (TA) muscles were recorded using surface electrode. Onset latencies, durations, and amplitudes of the LLR were measured. The LLR on the unaffected side was obtained in all subjects. The LLR latencies were delayed, and amplitudes were small when only the unilateral leg was perturbated in healthy subjects. In stroke patients, the perturbation of the affected leg could evoke LLRs in both sides of the TA, although the LLR obtained in the affected side was delayed. The onset latencies were 290 msec on the affected side and 150 msec on the unaffected side. The LLR on the affected side was abolished when the unaffected side platform was tilted. These LLR abnormalities may arise from the poor balance caused by spasticity or the cortical loop lesion.