25 patients with hemiparesis and without overt mirror movements were examined. EMG needle electrodes were inserted into the opponens pollicis and abductor digiti minimi muscles of the affected hand and the EMG recording was filmed during opposition of the thumb and abduction of the fifth finger of the intact hand. In 10 patients action potentials were recorded from both examined muscles. The study shows that muscle contractions equivalent to overt mirror movements are a frequent finding in hemiplegia.